MERGER PROPOSED—YOUR VOTE IS VERY IMPORTANT

The board of directors of Fairmount Santrol Holdings Inc. (the “Fairmount Board”) cordially invites you to attend a special meeting of Fairmount Santrol Holdings Inc., a Delaware corporation (“Fairmount Santrol”), stockholders to be held at Jones Day located at 901 Lakeside Avenue, Cleveland, Ohio 44114 on May 25, 2018, at 1:30 p.m., Eastern Time (such meeting, including any adjournment or postponement thereof, the “special meeting”). As previously announced, on December 11, 2017, Fairmount Santrol entered into an Agreement and Plan of Merger, by and among SCR-Sibelco NV, a privately-owned Belgian company (“Sibelco”), Unimin Corporation, a Delaware corporation (“Unimin”), Bison Merger Sub, Inc., a Delaware corporation and direct wholly owned subsidiary of Unimin (“Merger Sub”), and Bison Merger Sub I, LLC, a Delaware limited liability company and direct wholly owned subsidiary of Unimin (as it may be amended from time to time, the “Merger Agreement”), providing for, among other things, the merger (the “Merger”) of Merger Sub into Fairmount Santrol with Fairmount Santrol continuing as the surviving corporation and a direct wholly owned subsidiary of Unimin.

At the special meeting, you will be asked to consider and vote on:

The Fairmount Board has determined that entering into the Merger Agreement and consummating the transactions contemplated by the Merger Agreement, including the Merger, are advisable, fair to and in the best interests of, Fairmount Santrol and Fairmount Santrol stockholders and recommends that Fairmount Santrol stockholders vote (1) “FOR” the Fairmount Santrol Merger proposal, (2) “FOR” the Fairmount Santrol compensation proposal and (3) “FOR” the Fairmount Santrol adjournment proposal.

Upon the closing of the Merger, Unimin will become the parent holding company for the combined group (referred to herein as the “combined company”) and will operate under a new name that will be selected by Unimin and Fairmount Santrol prior to the closing of the Merger. Each Fairmount Santrol stockholder will be entitled to receive (i) the number of shares of combined company common stock that will result in Fairmount Santrol stockholders, together with the holders of certain Fairmount Santrol equity awards, owning approximately 35% of the combined company common stock, (ii) an amount in cash equal to the result of (x) $170,000,000, divided by (y) the fully diluted Fairmount Santrol share number, without interest (which is estimated to result in cash consideration of approximately $0.74 per fully diluted share of Fairmount Santrol common stock), and (iii) cash paid in lieu of fractional shares, if any, without interest. The total number of shares of Unimin common stock that we estimate will be issued to Fairmount Santrol stockholders in connection with the Merger is 48,275,651 (which includes 44,990,934 shares to be issued to existing Fairmount Santrol stockholders and 3,284,717 shares to be reserved for issuance to holders of certain Fairmount Santrol equity awards), based on the number of Fairmount Santrol shares outstanding on April 2, 2018, with each Fairmount Santrol stockholder entitled to one whole share of Unimin common stock for every five whole shares of Fairmount Santrol common stock owned at the effective time. At the time of the special meeting, you will not know or be able to determine the value of the combined company stock you would receive upon the closing of the Merger for reasons further described in this proxy statement/prospectus. Immediately following the effective time of the Merger (the “effective time”), Sibelco will own, directly or indirectly, approximately 65% of the shares of combined company common stock and Fairmount Santrol stockholders, including holders of certain Fairmount Santrol equity awards, immediately prior to the effective time will own the remaining approximately 35% of the outstanding shares. Each outstanding Fairmount Santrol Stock Option, Fairmount Santrol RSU and Fairmount Santrol PSU will automatically convert into stock options and RSUs with respect to combined company common stock,

on the same terms and conditions under the applicable plans and award agreements in effect immediately prior to the

effective time after giving effect to the Exchange Ratio (as defined below under “The Merger Agreement—Effects of the Merger; Merger Consideration”) and appropriate adjustments to reflect the closing of the Merger. Following the closing of the Merger, the combined company expects to become a publicly-traded company with its common stock listed on the New York Stock Exchange (the “NYSE”) under a trading symbol to be mutually selected by Unimin and Fairmount Santrol. Unimin and Fairmount Santrol are unable to determine with reasonable certainty the anticipated time period between the special meeting and the effective time due to their inability to reasonably anticipate when foreign regulatory approval will be obtained.

As described in this proxy statement/prospectus, certain Fairmount Santrol stockholders who in the aggregate own approximately 26% of the outstanding shares of Fairmount Santrol common stock entered into a voting and support agreement with Unimin and Merger Sub, dated December 11, 2017, whereby such stockholders agreed to vote in favor of the Fairmount Santrol Merger proposal and against actions that could adversely affect the closing of the Merger.

Your vote is very important, regardless of the number of shares you own. The Merger cannot be completed unless stockholders holding at least a majority of the shares of Fairmount Santrol common stock outstanding as of the close of business on April 20, 2018, the record date for the special meeting, vote in favor of the Fairmount Santrol Merger proposal. A failure to vote or an abstention will have the same effect as a vote “AGAINST” the Fairmount Santrol Merger proposal.

Whether or not you plan to attend the special meeting, I urge you to vote your shares before the special meeting over the Internet or via the toll-free telephone number, as described in the accompanying materials. You may also vote by mail by completing, signing and dating the enclosed proxy card and returning it in the pre-addressed, postage-prepaid envelope accompanying the proxy card. YOUR PROXY IS BEING SOLICITED BY THE FAIRMOUNT BOARD. AFTER CAREFUL CONSIDERATION, THE FAIRMOUNT BOARD HAS (I) APPROVED THE MERGER AGREEMENT, (II) DETERMINED THAT ENTERING INTO THE MERGER AGREEMENT AND CONSUMMATING THE TRANSACTIONS CONTEMPLATED BY THE MERGER AGREEMENT, INCLUDING THE MERGER, ARE ADVISABLE, FAIR TO AND IN THE BEST INTERESTS OF FAIRMOUNT SANTROL AND FAIRMOUNT SANTROL STOCKHOLDERS AND AUTHORIZED AND APPROVED THE EXECUTION, DELIVERY AND PERFORMANCE OF THE MERGER AGREEMENT AND (III) DIRECTED THAT THE MERGER AGREEMENT BE SUBMITTED FOR CONSIDERATION BY FAIRMOUNT SANTROL STOCKHOLDERS. THE FAIRMOUNT BOARD RECOMMENDS THAT YOU VOTE (1) “FOR” THE FAIRMOUNT SANTROL MERGER PROPOSAL, (2) “FOR” THE FAIRMOUNT SANTROL COMPENSATION PROPOSAL AND (3) “FOR” THE FAIRMOUNT SANTROL ADJOURNMENT PROPOSAL. In considering the recommendation of the Fairmount Board, you should be aware that certain directors and executive officers of Fairmount Santrol may have interests in the Merger that are different from, or in addition to, the interests of Fairmount Santrol stockholders generally. See the section entitled “Interests of Fairmount Santrol’s Directors and Executive Officers in the Merger” beginning on page 171 of the accompanying proxy statement/prospectus.

I urge you to read carefully and in its entirety the accompanying proxy statement/prospectus, including the annexes and the documents incorporated by reference. In particular, I urge you to read carefully the section entitled “Risk Factors” beginning on page 46 of the accompanying proxy statement/prospectus. If you have any questions regarding the accompanying proxy statement/prospectus, you may call Georgeson LLC, Fairmount Santrol’s proxy solicitor, toll-free at (888) 877-5373.

Jenniffer D. Deckard

President and Chief Executive Officer

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED THE MERGER OR OTHER TRANSACTIONS DESCRIBED IN THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS OR THE SECURITIES TO BE ISSUED PURSUANT TO THE MERGER UNDER THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS NOR HAVE THEY DETERMINED IF THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS IS ACCURATE OR ADEQUATE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

This proxy statement/prospectus is dated April 26, 2018 and is first being mailed or otherwise delivered to Fairmount Santrol stockholders on or about April 26, 2018.

Fairmount Santrol Holdings Inc.

8834 Mayfield Road

Chesterland, Ohio 44026

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS TO BE HELD ON MAY 25, 2018

Dear Stockholder,

You are cordially invited to attend a special meeting (such meeting, including any adjournment or postponement thereof, the “special meeting”) of Fairmount Santrol Holdings Inc., a Delaware corporation (“Fairmount Santrol”), stockholders. The special meeting will be held at Jones Day located at 901 Lakeside Avenue, Cleveland, Ohio 44114 on May 25, 2018, at 1:30 p.m., Eastern Time, to consider and vote upon the following matters:

The record date of the special meeting is April 20, 2018. Only stockholders of record as of the close of business on April 20, 2018 are entitled to notice of, and to vote at, the special meeting. All stockholders of record as of that date and time are cordially invited to attend the special meeting in person. At the close of business on the record date, Fairmount Santrol had 224,982,895 shares of common stock outstanding and entitled to vote.

Your vote is very important, regardless of the number of shares of Fairmount Santrol common stock that you own. The Merger cannot be completed unless the Fairmount Santrol Merger proposal is approved by the stockholders holding at least a majority of the shares of Fairmount Santrol common stock outstanding as of the close of business on the record date. Whether or not you plan to attend the special meeting, Fairmount Santrol urges you to vote your shares before the special meeting over the Internet or via the toll-free telephone number, as described in the accompanying materials. You may also vote by mail by completing, signing and dating the enclosed proxy card and returning it in the pre-addressed, postage-prepaid envelope accompanying the proxy card. No postage is necessary if mailed in the United States. Voting over the Internet, via the toll-free telephone number or by mailing a proxy card will not limit your right to vote in person or to attend the special meeting. If you hold your shares in “street name” through a bank, brokerage firm or other nominee, you should follow the procedures provided by your bank, brokerage firm or other nominee to vote your shares. If you fail to submit a proxy or to attend the special meeting in person or do not provide your bank, brokerage firm or other nominee

with instructions as to how to vote your shares, as applicable, your bank, brokerage firm or other nominee will not have the authority to vote on any of the proposals on your behalf and your shares of Fairmount Santrol common stock will not be counted for purposes of determining whether a quorum is present at the special meeting and will have the same effect as a vote “AGAINST” the Fairmount Santrol Merger proposal.

Your proxy is being solicited by the board of directors of Fairmount Santrol (the “Fairmount Board”). After careful consideration, the Fairmount Board has (i) approved the Merger Agreement, (ii) determined that entering into the Merger Agreement and consummating the transactions contemplated by the Merger Agreement, including the Merger, are advisable, fair to and in the best interests of Fairmount Santrol and Fairmount Santrol stockholders and authorized and approved the execution, delivery and performance of the Merger Agreement and (iii) directed that the Merger Agreement be submitted for consideration by Fairmount Santrol stockholders.

The Fairmount Board recommends that Fairmount Santrol stockholders vote (1) “FOR” the Fairmount Santrol Merger proposal, (2) “FOR” the Fairmount Santrol compensation proposal and (3) “FOR” the Fairmount Santrol adjournment proposal. In considering the recommendation of the Fairmount Board, you should be aware that certain directors and executive officers of Fairmount Santrol may have interests in the Merger that are different from or in addition to the interests of Fairmount Santrol stockholders generally. See the section entitled “Interests of Fairmount Santrol’s Directors and Executive Officers in the Merger” beginning on page 171 of the accompanying proxy statement/prospectus.

If you personally attend the special meeting, you will be asked to verify that you are a stockholder by presenting an attendance ticket (attached to your proxy card), together with a proper form of identification. Cameras, recording devices and other electronic devices, including telephones or other devices with photographic capability, may not be used during the special meeting and are subject to confiscation. For the safety of attendees, all bags, packages and briefcases are subject to inspection. Your compliance is appreciated.

IT IS IMPORTANT THAT YOU VOTE YOUR SHARES OF FAIRMOUNT SANTROL COMMON STOCK PROMPTLY. WHETHER OR NOT YOU PLAN TO ATTEND THE SPECIAL MEETING, PLEASE VOTE YOUR SHARES BEFORE THE SPECIAL MEETING OVER THE INTERNET OR VIA THE TOLL-FREE TELEPHONE NUMBER OR BY COMPLETING, SIGNING AND DATING THE ENCLOSED PROXY CARD AND RETURNING IT IN THE PRE-ADDRESSED, POSTAGE-PREPAID ENVELOPE ACCOMPANYING THE PROXY CARD. IF YOU ATTEND THE SPECIAL MEETING AND VOTE IN PERSON, YOUR VOTE BY BALLOT WILL REVOKE ANY PROXY PREVIOUSLY SUBMITTED.

By Order of the Board of Directors,

Jenniffer D. Deckard

President and Chief Executive Officer

Chesterland, Ohio

Dated: April 26, 2018

ADDITIONAL INFORMATION

This proxy statement/prospectus incorporates important business and financial information about Fairmount Santrol from other documents that Fairmount Santrol has filed with the U.S. Securities and Exchange Commission (the “SEC”) and that are incorporated by reference herein. For a listing of documents incorporated by reference herein, please see the section entitled “Where You Can Find Additional Information” beginning on page 372 of this proxy statement/prospectus. This information is available for you to review at the SEC’s public reference room located at 100 F Street, N.E., Room 1580, Washington, DC 20549, and through the SEC’s website at www.sec.gov.

You may request copies of this proxy statement/prospectus and any of the documents incorporated by reference herein, without charge, by written or oral request directed to:

Attention: Secretary

Fairmount Santrol Holdings Inc.

8834 Mayfield Road

Chesterland, Ohio 44026

(800) 255-7263

In order for you to receive timely delivery of the documents in advance of the special meeting of Fairmount Santrol stockholders to be held on May 25, 2018 (such meeting, including any adjournment or postponement thereof, the “special meeting”), you must request the information no later than 10 business days prior to the date of the special meeting, by May 11, 2018.

Investors may also consult Fairmount Santrol’s website for more information concerning the Merger described in this proxy statement/prospectus. Fairmount Santrol’s website is fairmountsantrol.com. Information included on the Fairmount Santrol website is not incorporated by reference into this proxy statement/prospectus.

ABOUT THE PROXY STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by Unimin (File No. 333-224228), constitutes a prospectus of Unimin under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), and the rules and regulations promulgated thereunder, with respect to the combined company common stock to be issued to Fairmount Santrol stockholders pursuant to the Merger Agreement. The term “combined company” as used in this proxy statement/prospectus refers to Unimin following the closing of the Merger, which will operate under a new name that will be selected by Unimin and Fairmount Santrol prior to the closing of the Merger. This document also constitutes a proxy statement of Fairmount Santrol under Section 14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Additionally, this document constitutes a notice of meeting with respect to the special meeting at which Fairmount Santrol stockholders will be asked to consider and vote upon the Fairmount Santrol Merger proposal and related matters.

Fairmount Santrol has supplied all information contained in or incorporated by reference into this proxy statement/prospectus relating to Fairmount Santrol, and Unimin has supplied all information contained in this proxy statement/prospectus relating to Unimin and Sibelco.

You should rely only on the information contained in or incorporated by reference into this proxy statement/prospectus. Unimin and Fairmount Santrol have not authorized anyone to provide you with information that is different from that contained in or incorporated by reference into this proxy statement/prospectus. This proxy statement/prospectus is dated April 26, 2018, and you should not assume that the information contained herein is accurate as of any date other than such date. Further, you should not assume that the information contained in any document incorporated by reference into this proxy statement/prospectus is accurate as of any date other than the date of such incorporated document. Neither the mailing of this proxy statement/prospectus to Fairmount Santrol stockholders nor the issuance by the combined company of shares of combined company common stock pursuant to the Merger Agreement will create any implication to the contrary.

The information in this proxy statement/prospectus is subject to completion. A registration statement relating to the securities described herein has been filed with the SEC. These securities may not be sold nor

may offers to buy these securities be accepted prior to the time the registration statement becomes effective. This proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction to or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction, nor shall there be any sale of these securities in any jurisdiction, in which such offer would be unlawful prior to registration under the securities laws of such jurisdiction.

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QUESTIONS AND ANSWERS

The following are some questions that you, as a stockholder of Fairmount Santrol, may have regarding the Merger and the other matters being considered at the special meeting, as well as the answers to those questions. Fairmount Santrol urges you to read carefully the section entitled “Summary” beginning on page 16 of this proxy statement/prospectus and the remainder of this proxy statement/prospectus because the information in this section does not provide all the information that might be important to you with respect to the Merger and the other matters being considered at the special meeting. Additional important information is also contained in the annexes to and the documents incorporated by reference into this proxy statement/prospectus.

You may obtain the information incorporated by reference into this proxy statement/prospectus without charge by following the instructions under the section entitled “Where You Can Find Additional Information” beginning on page 372 of this proxy statement/prospectus.

About the Merger

Q: Why am I receiving this proxy statement/prospectus and proxy card?

A: Fairmount Santrol has agreed to combine with Unimin under the terms of the Merger Agreement, as further described in this proxy statement/prospectus. If the Merger Agreement is approved by Fairmount Santrol stockholders and the other conditions to closing under the Merger Agreement are satisfied or waived, Bison Merger Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of Unimin (“Merger Sub”), will be merged with and into Fairmount Santrol, with Fairmount Santrol continuing as the surviving corporation (the “Merger”), followed immediately by the merger of Fairmount Santrol with and into Bison Merger Sub I, LLC, a Delaware limited liability company and a direct wholly owned subsidiary of Unimin (“Merger Sub LLC”), with Merger Sub LLC continuing as the surviving entity and a direct wholly owned subsidiary of Unimin (the “Second Merger” and, together with the Merger, the “Mergers”).

Fairmount Santrol is holding the special meeting to ask its stockholders to consider and vote upon (i) a proposal to adopt the Merger Agreement (the “Fairmount Santrol Merger proposal”), (ii) a non-binding, advisory proposal to approve the compensation that may become payable to Fairmount Santrol’s named executive officers in connection with the closing of the Merger, which compensation is summarized in the table below in the section entitled “Advisory Vote on Merger-Related Compensation for Fairmount Santrol’s Named Executive Officers” beginning on page 367 of this proxy statement/prospectus (the “Fairmount Santrol compensation proposal”), and (iii) a proposal to adjourn the special meeting, if necessary or appropriate, including to solicit additional proxies, if there are not sufficient votes to approve the Fairmount Santrol Merger proposal (the “Fairmount Santrol adjournment proposal”).

This proxy statement/prospectus contains important information about the Merger, the Merger Agreement, a copy of which is attached as Annex A to this proxy statement/prospectus, the special meeting and the proposals to be voted on at the special meeting. Fairmount Santrol stockholders should read this information carefully and in its entirety. The enclosed voting materials allow stockholders to vote their shares without attending the special meeting in person.

Q: What is the proposed merger on which I am being asked to vote?

A: Fairmount Santrol and Unimin have agreed to the strategic combination of Fairmount Santrol and Unimin under the terms of the Merger Agreement that is described in this proxy statement/prospectus. Subject to the terms and conditions of the Merger Agreement, Merger Sub will be merged with and into Fairmount Santrol, with Fairmount Santrol continuing as the surviving corporation, followed immediately by the merger of Fairmount Santrol with and into Merger Sub LLC, with Merger Sub LLC continuing as the surviving entity and a direct wholly owned subsidiary of Unimin. As a result of the Merger, each issued and outstanding share of Fairmount Santrol common stock will be converted into the right to receive the Merger Consideration, consisting of the Stock Consideration, the Cash Consideration (each as defined in the Merger Agreement) and cash paid in lieu of fractional shares, if any, without interest.

Upon the closing of the Merger, Unimin will be the parent holding company for the combined group (referred to herein as the “combined company”) and will operate under a new name that will be selected by

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Unimin and Fairmount Santrol prior to the closing of the Merger. As a result of the Merger, Fairmount Santrol will no longer be a publicly held company. Following the Merger, Fairmount Santrol common stock will be delisted from the NYSE and deregistered under the Exchange Act, and Fairmount Santrol will no longer be required under Sections 13 or 14 of the Exchange Act to file periodic reports and proxy statements and other information with the SEC in respect of Fairmount Santrol common stock. Following the Merger, the combined company will become a publicly traded company with its common stock listed on the NYSE and registered under the Exchange Act. The combined company will be subject to the reporting requirements of Sections 13 and 14 of the Exchange Act and will file periodic reports and proxy statements and other information with the SEC in respect of the combined company common stock.

Q: Why is stockholder approval necessary and who is entitled to vote?

A: This proxy statement/prospectus serves as the proxy statement through which Fairmount Santrol will solicit proxies to obtain the necessary stockholder approval for the Merger. It also serves as the prospectus by which Unimin will issue its common stock as consideration in the Merger. Fairmount Santrol is holding the special meeting in order to obtain the stockholder approval necessary to adopt the Merger Agreement. Fairmount Santrol will be unable to complete the Merger unless, among other things, the Fairmount Santrol stockholders vote in favor of the Fairmount Santrol Merger proposal.

You are receiving this proxy statement/prospectus because you were a holder of record of Fairmount Santrol common stock as of the close of business on April 20, 2018, the record date for the special meeting (the “record date”). This proxy statement/prospectus contains important information about the Merger, the Merger Agreement (which is summarized below in the section entitled “The Merger Agreement” and a copy of which is attached as Annex A), the Amended and Restated Certificate of Incorporation of Unimin and the Amended and Restated Bylaws of Unimin (which are summarized below in the sections entitled “Description of Combined Company Capital Stock” and “Comparison of Stockholder Rights Before and After the Merger” and forms of which are attached as Annexes C and D) and the special meeting. You should read this information carefully and in its entirety. The enclosed voting materials also allow you to vote your shares of Fairmount Santrol common stock without attending the special meeting. Your vote is very important and we encourage you to submit your proxy as soon as possible.

Q: What will Fairmount Santrol stockholders receive if the Merger is completed?

A: If the Merger is completed, each share of Fairmount Santrol common stock issued and outstanding immediately prior to the closing of the Merger (other than (1) shares owned by Fairmount Santrol or any wholly owned subsidiary of Fairmount Santrol (or held in the treasury of Fairmount Santrol), (2) shares owned by SCR-Sibelco NV, a privately-owned Belgian company (“Sibelco”) or any of its subsidiaries and (3) shares held by a stockholder who is entitled to appraisal rights and has properly exercised and perfected (and not effectively withdrawn or lost) such stockholder’s demand for appraisal rights under the General Corporation Law of the State of Delaware (the “DGCL”)) will be converted into the right to receive:

The Exchange Ratio is equal to 0.20. For purposes of estimating the Stock Consideration to which each Fairmount Santrol stockholder will be entitled at the effective time of the Merger (the “effective time”), for every five whole shares of Fairmount Santrol common stock owned as of the effective time, such stockholder would receive one whole share of combined company common stock. At the effective time, the combined company estimates that it will have outstanding or reserved for issuance approximately 134,252,401 shares of common

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stock, of which approximately 35% will be issued to Fairmount Santrol stockholders (or reserved for issuance for holders of Fairmount Santrol equity awards) as the Stock Consideration, and no shares of preferred stock. The total number of shares that the combined company expects to have outstanding or reserved for issuance as of the effective time is based on the number of shares of Fairmount Santrol common stock, Fairmount Santrol RSUs, Fairmount Santrol PSUs and Fairmount Santrol Stock Options outstanding as of December 8, 2017 plus an estimated number of shares of Fairmount Santrol common stock, Fairmount Santrol RSUs and Fairmount Santrol PSUs issued or to be issued (or cancelled) between December 8, 2017 and the effective time.

The Exchange Ratio has been agreed by Unimin and Fairmount Santrol in order to derive a market-appropriate number of shares of combined company common stock outstanding following the effective time. The Exchange Ratio, in combination with the number of shares of combined company common stock to be held by Sibelco following the effective time, will result in the Fairmount Santrol stockholders and equity award holders receiving approximately 35% of the issued and outstanding shares of combined company common stock, as required by the Merger Agreement. The 65% : 35% split between Sibelco and Fairmount Santrol stockholders was agreed in the Merger Agreement based on the fully diluted Fairmount Santrol share count as of December 8, 2017, where the Fairmount Santrol Stock Options included in such share count were calculated in accordance with the treasury method of accounting. The Fairmount Santrol stockholders will own approximately 35% of the shares of combined company common stock issued and outstanding, regardless of the aggregate combined company share count as of the effective time.

For purposes of estimating the Cash Consideration to which each Fairmount Santrol stockholder will be entitled at the effective time, the fully diluted Fairmount Santrol share number calculated as of April 2, 2018 was 230,992,325. The fully diluted Fairmount Santrol share number is not expected to be materially different at the effective time.

The Stock Consideration, the Cash Consideration and the right to receive cash in lieu of fractional shares, if any, are collectively referred to in this proxy statement/prospectus as the “Merger Consideration.” For more information about the Merger Consideration, see the section entitled “The Merger Agreement—Effects of the Merger; Merger Consideration” beginning on page 186 of this proxy statement/prospectus.

Q: What equity stake will Fairmount Santrol stockholders hold in the combined company immediately following the Merger?

A: Holders of shares of Fairmount Santrol common stock as of immediately prior to the effective time will hold, in the aggregate, together with holders of certain Fairmount Santrol equity awards, approximately 35% of the issued and outstanding shares of combined company common stock immediately following the closing of the Merger. Approximately 65% of the combined company common stock will be owned, directly or indirectly, by Sibelco, which is currently Unimin’s parent company and owns, directly or indirectly, 100% of Unimin common stock. The combined company will be a “controlled company” within the meaning of the rules of the NYSE and intends to rely on exemptions from certain corporate governance requirements available to controlled companies. As a result of their reduced ownership percentage, former Fairmount Santrol stockholders will have less voting power in the combined company than they now have with respect to Fairmount Santrol and will not have the ability to control the outcome of matters voted upon by all of the combined company stockholders.

Q: How will I receive the Merger Consideration to which I am entitled?

A: After receiving the proper documentation from you, following the closing of the Merger, the exchange agent will forward to you the shares of combined company common stock, the Cash Consideration and cash in lieu of fractional shares, if any, to which you are entitled. If you own Fairmount Santrol common stock in book-entry form or through a bank, brokerage firm or other holder of record, you will not need to obtain share certificates to submit for exchange to the exchange agent, nor will you receive certificated shares of the combined company common stock. However, you or your bank, brokerage firm or other nominee will need to follow the instructions provided by the exchange agent in order to properly surrender your Fairmount Santrol common stock. More information on the documentation you are required to deliver to the exchange agent may be found in the section entitled “The Merger Agreement—Exchange of Fairmount Santrol Shares” beginning on page 187 of this proxy statement/prospectus.

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Q: Who is the exchange agent for the Merger?

A: American Stock Transfer & Trust Company, LLC is the exchange agent.

Q: Where will the shares of combined company common stock that I receive in the Merger be publicly traded?

A: Unimin has applied to the NYSE to list its shares of common stock, which will become shares of the combined company common stock, under a trading symbol to be mutually selected by Unimin and Fairmount Santrol. The listing of the combined company common stock on the NYSE is one of the closing conditions under the Merger Agreement. See the section entitled “The Merger Agreement—Conditions to Closing of the Merger” beginning on page 203 of this proxy statement/prospectus.

Q: Will my shares of combined company common stock acquired in the Merger receive dividends?

A: The combined company does not currently expect to pay dividends following the closing of the Merger. Any future determination of the combined company to issue dividends will remain subject to consideration and approval by the board of directors of the combined company (the “Combined Company Board”). The Combined Company Board will have sole discretion to determine whether any dividends will be declared, the amount of such dividends and when any dividend will be paid. Any determination to declare and pay dividends will be subject to a number of considerations, including, but not limited to, the combined company’s results of operations, the combined company’s liquidity and financing plans, the market price of the combined company common stock and the combined company’s access to capital markets, as well as legal requirements, industry practice and other factors deemed relevant by the Combined Company Board.

After the closing of the Merger, if any dividends are declared or paid by the combined company after the effective time, as a holder of shares of combined company common stock, you will be entitled to receive the same dividends on shares of combined company common stock that all other holders of combined company common stock will receive for any dividend record date that occurs after the Merger is consummated, subject to the following.

If any dividends are declared or paid by the combined company after the effective time, stockholders who held Fairmount Santrol common stock immediately prior to the closing of the Merger will not be entitled to be paid dividends otherwise payable on the shares of combined company common stock into which their shares of Fairmount Santrol common stock are exchangeable until such stockholder completes the appropriate documentation provided by the exchange agent and surrenders his or her Fairmount Santrol share certificates, if applicable, according to the instructions provided to him or her. Any such dividends will be accrued for these stockholders and they will receive the accrued dividends when they surrender their Fairmount Santrol share certificates, if applicable, subject to abandoned property laws. Former Fairmount Santrol stockholders will also receive any dividends with a record date prior to the closing of the Merger that have been declared by Fairmount Santrol with respect to the shares of Fairmount Santrol common stock but that have not been paid on those shares of Fairmount Santrol common stock that they hold.

Q: Who will serve as the directors and senior officers of the combined company?

A: Under the terms of the Merger Agreement, at the effective time, the Combined Company Board will consist initially of 11 directors. Six of the 11 directors will be selected by Unimin (one of whom will be the chairman of the Combined Company Board) and four of the 11 directors will be selected by Fairmount Santrol. The eleventh director will be the Chief Executive Officer of the combined company. At least three of the directors selected by Fairmount Santrol must be independent in accordance with the standards of the NYSE.

Jenniffer D. Deckard, currently the Chief Executive Officer of Fairmount Santrol, will be the Chief Executive Officer of the combined company, and, as such, Ms. Deckard will be a director on the Combined Company Board. The broader executive leadership team of the combined company will include a combination of existing leaders from both Unimin and Fairmount Santrol.

Q: When do you expect the Merger to be completed?

A: Subject to the satisfaction or waiver of the closing conditions described under the section entitled “The Merger Agreement—Conditions to Closing of the Merger” beginning on page 203 of this proxy statement/prospectus, including approval of the Fairmount Santrol Merger proposal by Fairmount Santrol stockholders at

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the special meeting and subject to receipt of applicable regulatory approvals, Fairmount Santrol and Unimin intend to complete the Merger as soon as reasonably practicable. Subject to the foregoing, Fairmount Santrol and Unimin currently expect to consummate the Merger in mid-2018. However, it is possible that factors outside the control of both companies could result in the Merger being completed at a different time or not at all. In addition, there may be a substantial amount of time between the special meeting and the closing of the Merger. For additional information on the regulatory approvals required to complete the Merger, see the section entitled “The Merger Agreement—Regulatory Approvals” beginning on page 199 of this proxy statement/prospectus.

Q: What effects will the Merger have on Fairmount Santrol?

A: Upon the closing of the Merger, Fairmount Santrol will cease to have its common stock traded publicly. Merger Sub will be merged with and into Fairmount Santrol, with Fairmount Santrol continuing as the surviving corporation, followed immediately by the merger of Fairmount Santrol with and into Merger Sub LLC, with Merger Sub LLC continuing as the surviving entity and a direct wholly owned subsidiary of the combined company. Following the closing of the Merger, the registration of Fairmount Santrol common stock and the reporting obligations of Fairmount Santrol with respect to its common stock under the Exchange Act will be terminated. In addition, following the closing of the Merger, shares of Fairmount Santrol common stock will no longer be listed on the NYSE or any other stock exchange or quotation system. Although current Fairmount Santrol stockholders will no longer be stockholders of Fairmount Santrol, they will have an indirect interest in Fairmount Santrol (or its successor) through their ownership of combined company common stock, which will be listed on the NYSE.

Q: What are the conditions to the closing of the Merger?

A: In addition to obtaining Fairmount Santrol stockholder approval (as defined herein), the obligations of Fairmount Santrol, Unimin and the other parties to the Merger Agreement to close the Merger are subject to the satisfaction or waiver of a number of other conditions, including, among others:

In addition, conditions to the obligations of Sibelco, Unimin, Merger Sub and Merger Sub LLC to close the Merger include, among others:

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In addition, conditions to the obligations of Fairmount Santrol to close the Merger include, among others:

For additional information on the regulatory approvals and clearances required to complete the Merger, see the section entitled “The Merger—Regulatory Approvals” beginning on page 199 of this proxy statement/prospectus. For additional information on the conditions to closing of the Merger, see the section entitled “The Merger Agreement—Conditions to Closing of the Merger” beginning on page 203 of this proxy statement/prospectus.

Q: What happens if the Merger is not completed?

A: If the Fairmount Santrol Merger proposal is not approved by Fairmount Santrol stockholders or if the Merger is not completed for any other reason, Fairmount Santrol stockholders will not receive any consideration for their shares of Fairmount Santrol common stock. Instead, Fairmount Santrol will remain an independent public company, Fairmount Santrol common stock will continue to be listed and traded on the NYSE and registered under the Exchange Act, and Fairmount Santrol will continue to file periodic reports with the SEC. Under certain circumstances, Fairmount Santrol may be required to pay Unimin a termination fee of $52 million. In other circumstances, Unimin may be required to pay Fairmount Santrol a termination fee of $52 million. See the sections entitled “The Merger Agreement—Termination,” “The Merger Agreement—Effect of Termination” and “The Merger Agreement—Termination Fees” beginning on pages 205, 207 and 208, respectively, of this proxy statement/prospectus.

Q: What will happen to outstanding Fairmount Santrol equity awards in the Merger?

A: The Merger Agreement generally provides for the conversion of Fairmount Santrol Stock Options, Fairmount Santrol RSU awards and Fairmount Santrol PSU awards into corresponding awards for a number of shares of combined company common stock determined by multiplying the number of shares of Fairmount Santrol common stock subject to each Fairmount Santrol equity award by the Exchange Ratio. The exercise price of the Fairmount Santrol Stock Options following the conversion will be determined by dividing the per-share exercise price of the Fairmount Santrol Stock Options by the Exchange Ratio. The converted Fairmount Santrol equity awards will be subject to the same terms and conditions as the original Fairmount Santrol equity awards, subject to certain exceptions. Holders of Fairmount Santrol RSU awards, Fairmount Santrol PSU awards and in-the-money Fairmount Santrol Stock Options will also be entitled to receive a portion of the Cash

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Consideration. For additional information on the treatment of Fairmount Santrol equity awards, see the section entitled “The Merger Agreement—Treatment of Fairmount Santrol Equity Awards” beginning on page 188 of this proxy statement/prospectus.

Q: Are there any risks related to the Merger or the combined business that I should consider?

A: Yes. There are risks associated with all mergers. These risks are discussed in more detail in the section entitled “Risk Factors” beginning on page 46 of this proxy statement/prospectus and you should also refer to the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 94 of this proxy statement/prospectus. You also should read and carefully consider the risk factors contained in the documents filed by Fairmount Santrol with the SEC that are incorporated by reference into this proxy statement/prospectus.

Q: Are Fairmount Santrol stockholders entitled to appraisal rights?

A: Yes, subject to compliance with the DGCL. Subject to the closing of the Merger, record holders of Fairmount Santrol common stock who do not vote in favor of the Fairmount Santrol Merger proposal and who otherwise properly exercise and perfect their appraisal rights in accordance with Section 262 of the DGCL (“Section 262”) will be entitled to seek appraisal for, and obtain payment in cash for the judicially determined fair value of, their shares of Fairmount Santrol common stock, in lieu of receiving the Merger Consideration. The “fair value” could be higher or lower than, or the same as, the Merger Consideration. For more information regarding appraisal rights, see the section entitled “Appraisal Rights of Fairmount Santrol Stockholders” beginning on page 361 of this proxy statement/prospectus. Failure to strictly comply with Section 262 may result in a waiver of, or inability to exercise, appraisal rights. The full text of Section 262 is attached as Annex E to this proxy statement/prospectus.

Q: Will Fairmount Santrol still have an annual stockholders’ meeting in 2018?

A: Fairmount Santrol does not expect to hold an annual stockholders’ meeting in 2018 while the Merger is pending, and it currently plans to delay its 2018 annual stockholders’ meeting and only hold an annual meeting in 2018 if the Merger is terminated or if the annual meeting is required by law.

Q: What are the material United States federal income tax consequences of the Mergers to Fairmount Santrol stockholders?

A: Assuming the Mergers, taken together as an integrated transaction, qualify as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Code”), a U.S. holder exchanging its shares of Fairmount Santrol common stock for a combination of combined company common stock and cash (including cash received in lieu of fractional shares, if any) pursuant to the Merger Agreement will generally recognize gain (but not loss) in an amount equal to the lesser of (i) the excess of such U.S. holder’s “amount realized” in the transaction (i.e., the fair market value of the shares of combined company common stock at the effective time plus the amount of cash (including cash received in lieu of fractional shares, if any) received by such U.S. holder in exchange for its shares of Fairmount Santrol common stock in the Merger) over such U.S. holder’s tax basis in its surrendered shares of Fairmount Santrol common stock and (ii) the amount of cash (including cash received in lieu of fractional shares, if any) received by such U.S. holder in exchange for its shares of Fairmount Santrol common stock in the Merger. Assuming the Mergers qualify as a “reorganization” within the meaning of Section 368(a) of the Code, non-U.S. holders are generally not expected to be subject to U.S. federal income tax in respect of the Mergers, subject to certain exceptions, including those relating to tax imposed under the Foreign Investment in Real Property Tax Act (“FIRPTA”). For a more complete description of the U.S. federal income tax consequences of the Mergers, see the section entitled “Material United States Federal Income Tax Consequences of the Transaction” beginning on page 178 of this proxy statement/prospectus.

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About the Special Meeting

Q: When and where is the special meeting?

A: The special meeting will be held on May 25, 2018, at 1:30 p.m., Eastern time, at Jones Day located at 901 Lakeside Avenue, Cleveland, Ohio 44114. If you personally attend the special meeting, you will be asked to verify that you are a Fairmount Santrol stockholder by presenting an attendance ticket (attached to your proxy card), together with a proper form of identification. If your shares of Fairmount Santrol common stock are held through a bank, brokerage firm or other nominee, please bring proof of your beneficial ownership of such shares to the special meeting. Acceptable proof could include an account statement showing that you owned shares of Fairmount Santrol common stock on the record date. For additional information about the special meeting, see the section entitled “The Special Meeting” beginning on page 116 of this proxy statement/prospectus.

Q: What is the record date?

A: The record date for determining holders of record for purposes of the special meeting is April 20, 2018.

Q: Who can vote at the special meeting?

A: All holders of record of shares of Fairmount Santrol common stock as of the close of business on the record date are entitled to receive notice of, and to vote at, the special meeting. Each holder of shares of Fairmount Santrol common stock is entitled to cast one vote on each matter properly brought before the special meeting for each share of Fairmount Santrol common stock that such holder owned of record as of the close of business on the record date.

Q: How can I attend the special meeting?

A: All stockholders will need proof of ownership of shares in Fairmount Santrol, and may be asked to present a form of personal photo identification, in order to be admitted to the special meeting. In addition, if your shares are held in the name of your bank, brokerage firm or other nominee and you wish to attend the special meeting, you must bring an account statement or letter from the bank, brokerage firm or other nominee indicating that you were the owner of the shares on the record date.

Q: What am I being asked to vote on at the special meeting?

A: You are being asked to consider and vote upon (i) the Fairmount Santrol Merger proposal, (ii) the Fairmount Santrol compensation proposal and (iii) the Fairmount Santrol adjournment proposal. The approval of the Fairmount Santrol compensation proposal is not a condition to the closing of the Merger and the Merger will be consummated regardless of whether the compensation arrangements are approved. Fairmount Santrol will transact no other business at the special meeting except such business as may properly be brought before the special meeting or any adjournment or postponement thereof.

Q: Does my vote matter?

A: Yes. Your vote is important. You are encouraged to submit your proxy as promptly as possible. The Merger cannot be completed unless the Fairmount Santrol Merger proposal is approved by the Fairmount Santrol stockholders. If you fail to submit a proxy or vote in person at the special meeting, abstain from voting or do not provide your bank, brokerage firm or other nominee with instructions, as applicable, this will have the same effect as a vote “AGAINST” the Fairmount Santrol Merger proposal. The board of directors of Fairmount Santrol (the “Fairmount Board”) recommends that Fairmount Santrol stockholders vote (1) “FOR” the Fairmount Santrol Merger proposal, (2) “FOR” the Fairmount Santrol compensation proposal and (3) “FOR” the Fairmount Santrol adjournment proposal.

Q: Did the Fairmount Board approve the Merger Agreement?

A: Yes. At a meeting on December 11, 2017, the Fairmount Board (i) approved the Merger Agreement, (ii) determined that entering into the Merger Agreement and consummating the transactions contemplated by the Merger Agreement, including the Merger, are advisable, fair to and in the best interests of Fairmount Santrol and Fairmount Santrol stockholders and authorized and approved the execution, delivery and performance of the

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Merger Agreement and (iii) directed that the Merger Agreement be submitted for consideration by Fairmount Santrol stockholders.

Q: How does the Fairmount Board recommend that I vote at the special meeting?

A: The Fairmount Board recommends that Fairmount Santrol stockholders vote:

See the sections entitled “The Merger—Fairmount Santrol’s Reasons for the Merger” and “The Merger—Recommendation of the Fairmount Board” beginning on page 143 and page 147, respectively, of this proxy statement/prospectus.

Q: How do I vote?

A: You can vote your shares of Fairmount Santrol common stock in the following ways, depending on whether you are a stockholder of record or a beneficial owner:

Stockholder of Record. If you are a stockholder of record, you may vote your shares of Fairmount Santrol common stock on matters presented at the special meeting in any of the following ways:

Beneficial Owner. If you are a beneficial owner, please refer to the instructions provided by your bank, brokerage firm or other nominee to see which of the above choices are available to you. Please note that if you are a beneficial owner and wish to vote in person at the special meeting, you must obtain a legal proxy from your bank, brokerage firm or other nominee.

Q: If a stockholder gives a proxy, how are the shares of Fairmount Santrol common stock voted?

A: Regardless of the method you choose to vote, the individuals named on the enclosed proxy card will vote your shares of Fairmount Santrol common stock in the way that you indicate. When completing the Internet or telephone processes or the proxy card, you may specify whether your shares of Fairmount Santrol common stock should be voted “FOR” or “AGAINST” or to “ABSTAIN” from voting on all, some or none of the specific items of business to come before the special meeting.

If you properly sign your proxy card but do not mark the boxes showing how your shares should be voted on a matter, the shares represented by your properly signed proxy will be voted “FOR” the Fairmount Santrol Merger proposal, “FOR” the Fairmount Santrol compensation proposal and “FOR” the Fairmount Santrol adjournment proposal.

Q: Should I send in my share certificates now?

A: No, please do NOT return your share certificate(s) with your proxy. If the Fairmount Santrol Merger proposal is approved by Fairmount Santrol stockholders, the Merger is completed and you hold physical share certificates, you will be sent a letter of transmittal as promptly as reasonably practicable after the closing of the Merger describing how you may exchange your shares of Fairmount Santrol common stock for the per share Merger Consideration. If your shares of Fairmount Santrol common stock are held in “street name” through a

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bank, brokerage firm or other nominee, you will receive instructions from your bank, brokerage firm or other nominee as to how to effect the surrender of your “street name” shares of Fairmount Santrol common stock in exchange for the per share Merger Consideration.

Q: What is the vote required to approve each proposal at the special meeting?

A: Fairmount Santrol Merger Proposal. Approving the Fairmount Santrol Merger proposal requires the affirmative vote of the stockholders holding a majority of the outstanding shares of Fairmount Santrol common stock, at the close of business on the record date, entitled to vote on the Fairmount Santrol Merger proposal (“Fairmount Santrol stockholder approval”). Accordingly, if a Fairmount Santrol stockholder fails to submit a proxy or vote in person at the special meeting or abstains from voting, this will have the same effect as a vote “AGAINST” the Fairmount Santrol Merger proposal.

Fairmount Santrol Compensation Proposal. In accordance with Section 14A of the Exchange Act, Fairmount Santrol is providing stockholders with the opportunity to approve, by non-binding advisory vote, compensation payments for Fairmount Santrol’s named executive officers in connection with the Merger. Approving the Fairmount Santrol compensation proposal, on a non-binding advisory basis, requires the affirmative vote of a majority of Fairmount Santrol stockholders present, in person or represented by proxy, and entitled to vote at the special meeting. Accordingly, a Fairmount Santrol stockholder who attends the special meeting but does not vote will have the same effect as a vote “AGAINST” the Fairmount Santrol compensation proposal. Similarly, abstentions of Fairmount Santrol stockholders present, in person or represented by proxy, at the special meeting will have the same effect as a vote “AGAINST” the Fairmount Santrol compensation proposal. A Fairmount Santrol stockholder’s failure to submit a proxy card will have no effect on the Fairmount Santrol compensation proposal.

Fairmount Santrol Adjournment Proposal. Approving the Fairmount Santrol adjournment proposal requires the affirmative vote of a majority of Fairmount Santrol stockholders present, in person or represented by proxy, and entitled to vote at the special meeting. Accordingly, a Fairmount Santrol stockholder who attends the special meeting but does not vote will have the same effect as a vote “AGAINST” the Fairmount Santrol adjournment proposal. Similarly, abstentions of Fairmount Santrol stockholders present, in person or represented by proxy, at the special meeting will have the same effect as a vote “AGAINST” the Fairmount Santrol adjournment proposal.

See the section entitled “The Special Meeting—Record Date and Quorum” beginning on page 116 of this proxy statement/prospectus.

Q: How many votes do I have?

A: You are entitled to cast one vote for each share of Fairmount Santrol common stock that you owned as of the close of business on the record date. As of the close of business on the record date, there were 224,982,895 shares of Fairmount Santrol common stock issued and outstanding entitled to vote at the special meeting.

Q: Do the Fairmount Santrol stockholders have to vote on the Fairmount Santrol Merger proposal at the special meeting if the Fairmount Board has changed its recommendation with respect to the Fairmount Santrol Merger proposal?

A: Yes. Unless the Merger Agreement is terminated before the special meeting, Fairmount Santrol will notify the Fairmount Santrol stockholders before the special meeting if the Fairmount Board has changed its recommendation with respect to the adoption of the Merger Agreement, and the Fairmount Santrol stockholders will be asked to vote on the Fairmount Santrol Merger proposal even if the Fairmount Board has so changed its recommendation.

Q: What will happen if I am present at the special meeting, in person or by proxy, and I fail to vote or I abstain from voting?

A: Fairmount Santrol Merger Proposal. If you fail to submit a proxy or vote in person at the special meeting, abstain from voting or do not provide your bank, brokerage firm or other nominee with instructions, as applicable, this will have the same effect as a vote “AGAINST” the Fairmount Santrol Merger proposal.

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Fairmount Santrol Compensation Proposal. If you are a Fairmount Santrol stockholder present at the special meeting, in person or represented by proxy, and fail to vote or abstain, it will have the same effect as a vote “AGAINST” the Fairmount Santrol compensation proposal.

Fairmount Santrol Adjournment Proposal. If you are a Fairmount Santrol stockholder present at the special meeting, in person or represented by proxy, and fail to vote or abstain, it will have the same effect as a vote “AGAINST” the Fairmount Santrol adjournment proposal.

Q: What constitutes a quorum for the special meeting?

A: The presence at the special meeting, in person or represented by proxy, of holders of a majority of the shares of Fairmount Santrol common stock outstanding as of the close of business on the record date entitled to vote at the special meeting constitutes a quorum for the purposes of the special meeting. Abstentions will be counted in determining whether a quorum exists. If your shares are held in “street name” by your bank, brokerage firm or other nominee and you do not instruct your bank, brokerage firm or other nominee how to vote your shares, your bank, brokerage firm or other nominee will not have authority to vote on your behalf with respect to any of the proposals, and your shares will not be counted for purposes of determining whether a quorum exists. A quorum is necessary to transact business at the special meeting. Once a share of Fairmount Santrol common stock is represented at the special meeting, it will be counted for the purpose of determining a quorum at the special meeting and any adjournment of the special meeting. However, if a new record date is set for the adjourned special meeting, then a new quorum will be determined.

Q: What is the difference between holding shares as a stockholder of record and as a beneficial owner?

A: If your shares of Fairmount Santrol common stock are registered directly in your name with the transfer agent of Fairmount Santrol, American Stock Transfer & Trust Company, LLC, you are considered the stockholder of record with respect to those shares. As the stockholder of record, you have the right to vote or to grant a proxy for your vote directly to Fairmount Santrol or to a third party to vote at the special meeting.

If your shares of Fairmount Santrol common stock are held by a bank, brokerage firm or other nominee, you are considered the beneficial owner of shares held in “street name,” and your bank, brokerage firm or other nominee is considered the stockholder of record with respect to those shares. Your bank, brokerage firm or other nominee will send you, as the beneficial owner, a package describing the procedure for voting your shares of Fairmount Santrol common stock. You should follow the instructions provided by them to vote your shares of Fairmount Santrol common stock. You are invited to attend the special meeting; however, you may not vote these shares in person at the special meeting unless you obtain a “legal proxy” from your bank, brokerage firm or other nominee that holds your shares of Fairmount Santrol common stock, giving you the right to vote the shares of Fairmount Santrol common stock at the special meeting.

Q: If my shares of Fairmount Santrol common stock are held in “street name” by my bank, brokerage firm or other nominee, will my bank, brokerage firm or other nominee automatically vote those shares for me?

A: Your bank, brokerage firm or other nominee will only be permitted to vote your shares of Fairmount Santrol common stock if you instruct your bank, brokerage firm or other nominee how to vote. You should follow the procedures provided by your bank, brokerage firm or other nominee regarding the voting of your shares of Fairmount Santrol common stock. In accordance with the rules of the NYSE, banks, brokerage firms and other nominees who hold shares of Fairmount Santrol common stock in “street name” for their customers have authority to vote on “routine” proposals when they have not received instructions from beneficial owners.

However, banks, brokerage firms and other nominees are precluded from exercising their voting discretion with respect to non-routine matters, such as the Fairmount Santrol Merger proposal, the Fairmount Santrol compensation proposal and the Fairmount Santrol adjournment proposal.

As a result, absent specific instructions from you, banks, brokerage firms or other nominees are not empowered to vote your shares of Fairmount Santrol common stock at the special meeting. The effect of not instructing your bank, brokerage firm or other nominee how you wish your shares to be voted will be the same as

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a vote “AGAINST” the Fairmount Santrol Merger proposal, and assuming you are not present at the special meeting, in person or by proxy, will not have an effect on the Fairmount Santrol compensation proposal and the Fairmount Santrol adjournment proposal.

Please note that you may not vote shares of Fairmount Santrol common stock held in street name by returning a proxy card directly to Fairmount Santrol or by voting in person at the special meeting unless you provide a “legal proxy,” which you must obtain from your bank, brokerage firm, trust company or other nominee.

Q: What is a “broker non-vote”?

A: Under NYSE rules, banks, brokerage firms and other nominees may use their discretion to vote “uninstructed” shares (i.e., shares held of record by banks, brokerage firms or other nominees but with respect to which the beneficial owner of such shares has not provided instructions on how to vote on a particular proposal) with respect to matters that are considered to be “routine,” but not with respect to “non-routine” matters. “Non-routine” matters are matters that may substantially affect the rights or privileges of stockholders, such as mergers, stockholder proposals, elections of directors (even if not contested), executive compensation (including any advisory stockholder votes on executive compensation) and certain corporate governance proposals, even if management-supported. A “broker non-vote” occurs on an item when (i) a broker, nominee or intermediary has discretionary authority to vote on one or more proposals to be voted on at a meeting of stockholders, but is not permitted to vote on other proposals without instructions from the beneficial owner of the shares and (ii) the beneficial owner fails to provide the broker, nominee or intermediary with such instructions. Because none of the proposals to be voted on at the special meeting are “routine matters” for which your bank, brokerage firm or other nominee may have discretionary authority to vote, if you do not instruct your bank, brokerage firm or other nominee how to vote your shares, your bank, brokerage firm or other nominee will not have authority to vote on your behalf with respect to any of the proposals. Unless you attend the special meeting in person with a properly executed legal proxy from your bank, brokerage firm or other nominee, your failure to provide instructions to your bank, brokerage firm or other nominee will result in your shares of Fairmount Santrol common stock not being present and entitled to vote at the special meeting and not being voted on any of the proposals and your shares will not be counted for purposes of determining whether a quorum exists. Consequently, there cannot be any broker non-votes at the special meeting.

Q: How can I change or revoke my vote?

A: You have the right to revoke a proxy, whether delivered over the Internet, by telephone or by mail, at any time before it is exercised, by voting again at a later date through any of the methods available to you, by attending the special meeting and voting in person or by giving written notice of revocation to Fairmount Santrol prior to the time the special meeting begins. Written notice of revocation should be mailed to: Fairmount Santrol Holdings Inc., Attention: Secretary, 8834 Mayfield Road, Chesterland, Ohio 44026. Your attendance at the special meeting in and of itself will not revoke any proxy. For a full description of the mechanics of proxy submittals and revocations, see the section entitled “The Special Meeting—Voting Rights; Proxies; Revocation” beginning on page 117 of this proxy statement/prospectus.

Q: Are any Fairmount Santrol stockholders already committed to vote in favor of any of the special meeting proposals?

A: Yes. Concurrently with the entry into the Merger Agreement, Unimin and Merger Sub entered into a Voting and Support Agreement, dated December 11, 2017 (the “Voting and Support Agreement”), with ASP FML Holdings, LLC and Charles D. Fowler (collectively, the “Supporting Stockholders”). Under the Voting and Support Agreement, the Supporting Stockholders have agreed to vote all of their shares of Fairmount Santrol common stock (including all shares owned as of December 11, 2017 and any additional shares either Supporting Stockholder acquires before the special meeting) in favor of the Fairmount Santrol Merger proposal and have granted to Unimin a proxy to vote their shares in favor of the Fairmount Santrol Merger proposal. As of April 2, 2018, the Supporting Stockholders, collectively, beneficially owned (with sole or shared voting power) 59,304,771 shares, or approximately 26.4%, of the Fairmount Santrol common stock then outstanding. For more information, see “Voting and Support Agreement” beginning on page 211 of this proxy statement/prospectus.

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Q: What should I do if I receive more than one set of voting materials?

A: If you hold shares of Fairmount Santrol common stock in “street name” and also directly as a record holder or otherwise or if you hold shares of Fairmount Santrol common stock in more than one brokerage account, you may receive more than one set of voting materials relating to the special meeting. Please complete, sign, date and return each proxy card (or cast your vote by telephone or Internet as provided on your proxy card) or otherwise follow the voting instructions provided in this proxy statement/prospectus in order to ensure that all of your shares of Fairmount Santrol common stock are voted. If you hold your shares in “street name” through a bank, brokerage firm or other nominee, you should follow the procedures provided by your bank, brokerage firm or other nominee to vote your shares. If you hold your shares in “street name” through more than one bank, brokerage firm or other nominee, you should follow the procedures provided by each of your banks, brokerage firms or other nominees in respect of each set of voting materials to vote the portion of your shares of Fairmount Santrol common stock held through such bank, brokerage firm or other nominee.

Q: What happens if I sell my shares of Fairmount Santrol common stock before the special meeting?

A: The record date is earlier than both the date of the special meeting and the date on which the Merger will be completed. If you transfer your shares of Fairmount Santrol common stock after the record date but before the special meeting, you will, unless the transferee requests a proxy from you, retain your right to vote at the special meeting but will transfer the right to receive the per share Merger Consideration to the person to whom you transfer your shares. In order to receive the per share Merger Consideration, you must hold your shares at the time of the closing of the Merger.

Q: What happens if I sell or otherwise transfer my shares of Fairmount Santrol common stock after the special meeting but before the closing of the Merger?

A: If the Fairmount Santrol Merger proposal is approved by Fairmount Santrol stockholders at the special meeting and you sell or otherwise transfer your shares of Fairmount Santrol common stock after the special meeting but before the closing of the Merger, you will have transferred the right to receive the per share Merger Consideration to the person to whom you transfer your shares. In order to receive the per share Merger Consideration upon the closing of the Merger, you must hold your shares of Fairmount Santrol common stock at the time of the closing of the Merger.

Q: Who will solicit and pay the cost of soliciting proxies?

A: Fairmount Santrol is making this solicitation and will bear the expense of printing and mailing proxy materials to its stockholders. Fairmount Santrol will ask banks, brokers and other custodians, nominees and fiduciaries to send proxy materials to beneficial owners of shares of Fairmount Santrol common stock and to secure their voting instructions, if necessary, and Fairmount Santrol will reimburse them for their reasonable expenses in so doing. Fairmount Santrol’s directors, officers and employees may also solicit proxies personally or by telephone, but they will not be specifically compensated for soliciting proxies. Fairmount Santrol has retained Georgeson LLC, for a fee of up to $12,000 plus expenses, to aid in the solicitation of proxies by similar methods.

Q: Where can I find the voting results of the special meeting?

A: The preliminary voting results are expected to be announced at the special meeting. In addition, within four business days following certification of the final voting results, Fairmount Santrol intends to furnish on Form 8-K the final voting results of the special meeting with the SEC.

Q: What will happen if the Fairmount Santrol Merger proposal to be considered at the special meeting is not approved?

A: As a condition to the closing of the Merger, Fairmount Santrol stockholders must approve the Fairmount Santrol Merger proposal. Closing of the Merger is not conditioned or dependent on approval of any of the other proposals to be considered at the special meeting. See “The Merger Agreement—Conditions to Closing of the Merger” beginning on page 203 of this proxy statement/prospectus.

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Q: Why am I being asked to consider and vote on the proposal to approve, by non-binding, advisory vote, certain existing compensation arrangements for named executive officers of Fairmount Santrol in connection with the Merger?

A: Under SEC rules, Fairmount Santrol is required to seek a non-binding, advisory vote with respect to the compensation that may be paid or become payable to its named executive officers that is based on, or otherwise relates to, the Merger.

Q: What will happen if Fairmount Santrol stockholders do not approve this Merger-related executive compensation?

A: The vote on the Fairmount Santrol compensation proposal is a vote separate and apart from the vote on the Fairmount Santrol Merger proposal. Accordingly, Fairmount Santrol stockholders may vote in favor of the Fairmount Santrol Merger proposal and not in favor of the Fairmount Santrol compensation proposal, or vice versa. Fairmount Santrol stockholder approval of the compensation that may become payable to Fairmount Santrol’s named executive officers in connection with the closing of the Merger is not a condition to the closing of the Merger. The vote is an advisory vote and will not be binding on Fairmount Santrol or the combined company. If the Merger is completed, the Merger-related compensation may be paid to Fairmount Santrol’s named executive officers to the extent payable in accordance with the terms of their compensation agreements and arrangements even if Fairmount Santrol stockholders do not approve, by non-binding, advisory vote, the Merger-related executive compensation.

Q: Do any of Fairmount Santrol’s directors or executive officers have interests in the Merger that differ from or are in addition to my interests as a stockholder of Fairmount Santrol common stock?

A: In considering the recommendation of the Fairmount Board with respect to the Fairmount Santrol Merger proposal and the other matters described in this proxy statement/prospectus, you should be aware that certain directors and executive officers of Fairmount Santrol may have interests in the Merger that are different from, or in addition to, the interests of Fairmount Santrol stockholders generally. The Fairmount Board was aware of and has considered these interests, among other matters, in evaluating and negotiating the Merger Agreement and approving the Merger, and in recommending that the Merger Agreement be adopted by Fairmount Santrol stockholders. See the sections entitled “Interests of Fairmount Santrol’s Directors and Executive Officers in the Merger” beginning on page 171 of this proxy statement/prospectus and “Advisory Vote on Merger-Related Compensation for Fairmount Santrol’s Named Executive Officers” beginning on page 367 of this proxy statement/prospectus.

Q: What do I need to do now?

A: Even if you plan to attend the special meeting in person, after carefully reading and considering the information contained in this proxy statement/prospectus, please vote promptly to ensure that your shares are represented at the special meeting. If you hold your shares of Fairmount Santrol common stock in your own name as the stockholder of record, you may submit a proxy to have your shares of Fairmount Santrol common stock voted at the special meeting in one of three ways:

If you decide to attend the special meeting and vote in person, your vote by ballot will revoke any proxy previously submitted. If you are a beneficial owner, please refer to the instructions provided by your bank,

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brokerage firm or other nominee to see which of the above choices are available to you. Please note that if you are a beneficial owner and wish to vote in person at the special meeting, you must obtain a legal proxy from your bank, brokerage firm or other nominee.

Q: Who can help answer my questions?

A: Fairmount Santrol stockholders who have questions about the Merger Agreement, the Merger or the other matters to be voted on at the special meeting, who need assistance submitting their proxy or voting their shares or who desire additional copies of this proxy statement/prospectus or additional proxy cards should contact Fairmount Santrol’s proxy solicitor as follows:

Name: Georgeson LLC

Toll Free: (888) 877-5373

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