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ANNUAL REPORT PURSUANT TO SECTION 15(d) OF

THE SECURITIES EXCHANGE ACT OF 1934

            ¨    

TRANSITION REPORT PURSUANT TO SECTION 15(d) OF

THE SECURITIES EXCHANGE ACT OF 1934

U.S. BORAX INC.

401(k) PLAN FOR HOURLY EMPLOYEES

Financial Statements and Supplemental Schedules

As of December 31, 2007 and 2006

and for the Year Ended December 31, 2007

Together with Report of Independent Registered Public Accounting Firm

Report of Independent Registered Public Accounting Firm

Financial Statements:

Statements of Net Assets Available for Benefits as of December 31, 2007 and 2006

Statement of Changes in Net Assets Available for Benefits for the year ended December 31, 2007

Notes to Financial Statements

Supplemental Schedule*

Schedule H, Part IV, Line 4i-Schedule of Assets (Held at End of Year) as of December 31, 2007

Schedule H, Part IV, Line 4a-Schedule of Delinquent Contributions

Assets

Investments (at fair value)

Receivables:

Employee contributions

Employer contributions

Total receivables

Total assets

Liabilities

Excess contributions payable

Net assets available for benefits (at fair value)

Adjustment from fair value to contract value for fully
benefit-responsive investment contracts

Net assets available for benefits

See accompanying notes to financial statements.

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Additions to net assets attributed to:

Investment income:

Net appreciation in fair value of investments

Interest and dividends

Total investment income

Contributions:

Employee

Employer

Total contributions

Total additions

Deductions from net assets attributed to:

Benefits paid to participants

Transfers to the Rio Tinto America Inc. Savings Plan

Administrative expenses

Total deductions

Increase in net assets available for benefits

Net assets available for benefits:

Beginning of year

End of year

See accompanying notes to financial statements.

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1. Description of

    the Plan

The following brief description of the U.S. Borax Inc. 401(k) Plan for Hourly Employees (the Plan) is provided for general information purposes only. Participants should refer to the Plan document and summary plan description for more complete information.

General

The Plan is a defined contribution plan covering full-time hourly employees who are represented by or included in a collective bargaining unit of U.S. Borax Inc. and its affiliates (collectively, the “Company” or the “Employer”), as defined in the Plan document. U.S. Borax Inc. is an indirect, wholly-owned subsidiary of Rio Tinto America Inc., which is an indirect, wholly-owned subsidiary of Rio Tinto plc (the Parent). The Plan is intended to be a qualified retirement plan under the Internal Revenue Code (IRC) and is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA), as amended.

Eligible employees who are represented by Local 30-International Longshoremen’s and Warehousemen’s Union (Boron hourly employees) can participate in the Plan immediately after completing sixty days of continuous service.

Eligible employees who are represented by Local 20A-International Longshoremen’s and Warehousemen’s Union (Wilmington hourly employees) can participate in the Plan immediately upon employment.

Contributions

Each year participants may elect under a salary reduction agreement to contribute to the Plan. Contributions are limited by the IRC, which established a maximum contribution of $15,500 for the year ended December 31, 2007. Participant contributions are recorded in the period during which the amounts are withheld from participant earnings. Participants may also contribute amounts representing distributions from other qualified defined benefit or defined contribution plans.

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1. Description of

    the Plan

    Continued

Contributions – Continued

Boron hourly employees can contribute an amount not less than 1% and not more than 30% of their eligible compensation on a before-tax basis through payroll deductions. Participants may also elect to make an after-tax contribution not less than 1% and not more than 30% of their eligible compensation. Total before-tax and after-tax contributions cannot exceed 30% of each participant’s eligible compensation.

The Company matches the Boron participants’ contributions to the Plan at 30%, up to the first 5% of their eligible compensation. Matching contributions are recorded on the date the related participant contributions are withheld.

Wilmington hourly employees can contribute an amount not less than 1% and not more than 15% of their eligible compensation on a before-tax basis through payroll deductions. Participants may also elect to make an after-tax contribution not less than 1% and not more than 15% of their eligible compensation. Total before-tax and after-tax contributions cannot exceed 15% of each participant’s eligible compensation.

The Company matches the Wilmington participants’ contributions to the Plan at 35%, up to the first 5% of their eligible compensation. Matching contributions are recorded on the date the related participant contributions are withheld.

Participant Accounts

Individual accounts are maintained for each Plan participant. Each participant’s account is credited with the participant’s contributions, the Company’s matching contributions, and an allocation of the Plan’s earnings, and is charged with withdrawals and an allocation of the Plan’s losses and administrative expenses. Allocations are based on participant earnings or account balances, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s vested account.

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1. Description of

    the Plan

    Continued

Participant-Directed Options for Investments

Participants direct the investment of their contributions and the Company matching contributions into various investment options offered by the Plan. Investment options include a money market fund, common/collective trusts, mutual funds, synthetic guaranteed investment contracts and common stock of the Parent in the form of American Depositary Receipts (ADRs).

Vesting

Participants are immediately vested in their contributions and Company matching contributions plus actual earnings thereon.

Payment of Benefits

On termination of service due to death, disability, or retirement, participants or their beneficiaries may elect to receive lump-sum distributions or annual, semi-annual, quarterly or monthly installments in amounts equal to the value of the participants’ vested interests in their accounts. Under certain circumstances, participants may withdraw their contributions prior to the occurrence of these events.

Transfers

Along with the Plan, the Company also sponsors other 401(k) plans that cover represented employees. If employees are changed from union to non-union status during the year, their account balances are transferred from this Plan to the non-union plan. For the year ended December 31, 2007, transfers to the Rio Tinto America Inc. Savings Plan totaled $386,016.

2. Summary of

    Significant

    Accounting

    Policies

Basis of Presentation

The financial statements of the Plan have been prepared on the accrual basis of accounting.

Use of Estimates

The preparation of the Plan’s financial statements in conformity with accounting principles generally accepted in the United States of America requires Plan management to make estimates and assumptions that affect the reported amounts of net assets available for benefits at the date of the financial statements, the changes in net assets available for benefits during the reporting period and, when applicable, the disclosures of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates.

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2. Summary of

    Significant

    Accounting

    Policies

    Continued

Financial Accounting Standards Board Staff Position

As described in Financial Accounting Standards Board Staff Position, FSP AAG INV-1 and SOP 94-4-1, Reporting of Fully Benefit-Responsive Investment Contracts Held by Certain Investment Companies Subject to the AICPA Investment Company Guide and Defined-Contribution Health and Welfare and Pension Plans (the FSP), investment contracts held by a defined-contribution plan are required to be reported at fair value. However, contract value is the relevant measurement attribute for that portion of the net assets available for benefits of a defined-contribution plan attributable to fully benefit-responsive investment contracts because contract value is the amount participants would receive if they were to initiate permitted transactions under the terms of the plan. As required by the FSP, the Statement of Net Assets Available for Benefits presents the fair value of the investment contracts as well as the adjustment of the fully benefit-responsive investment contracts from fair value to contract value. The Statement of Changes in Net Assets Available for Benefits is prepared on a contract value basis.

Risks and Uncertainties

The Plan provides for investments in securities that are exposed to various risks, such as interest rate, currency exchange rate, credit and overall market fluctuation. Due to the level of risk associated with certain investment securities, it is reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants’ account balances and the amounts reported in the statements of net assets available for benefits.

Investment Valuation and Income Recognition

The Plan’s investments in mutual funds are valued at quoted market prices, which represent the net asset value of units held by the Plan at year end. Plan investments in common stock are stated at fair value based on quoted market prices. The Plan’s interest in the Dwight Stable Value Fund is valued based upon the market value of the underlying securities at quoted market value or quoted share prices. Participant loans are valued at their outstanding balances, which approximate fair value.

Purchases and sales of securities are recorded on a trade-date basis. Interest income is recorded on an accrual basis. Dividends are recorded on the ex-dividend date.

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2. Summary of

    Significant

    Accounting

    Policies

    Continued

Investment Valuation and Income Recognition - Continued

The net appreciation (depreciation) in the fair value of investments which includes realized gains (losses) and unrealized appreciation (depreciation) on those investments is shown in the statement of changes in net assets available for benefits of the Plan, and totaled $2,137,030 for the year ended December 31, 2007.

Payments of Benefits

Benefit payments are recorded when paid by the Plan.

Administrative Expenses

The Company pays the majority of the costs and expenses incurred in administering the Plan. The Company provides accounting and other services to the Plan at no cost to the Plan.

The Plan has several fund managers that manage the investments held by the Plan. During the year ended December 31, 2007, the Company paid all investment management fees related to this Plan.

The investment management fees related to transaction costs associated with the purchase or sale of Rio Tinto plc ADRs are paid by the participants.

Participant Loans

Participants may borrow from the Plan up to a maximum of $50,000 or 50% of their account balances, whichever is less. Each loan is secured by the balance in the participant’s account and bears interest at a rate commensurate with prevailing rates at the time funds are borrowed, as determined by the Plan Administrator. Loans originated during the year ended December 31, 2007 have interest rates set at prime plus one percent, and are reset quarterly.

3. Fully Benefit-

    Responsive

    Investment

    Contracts

The Plan’s investments include the Dwight Stable Value Fund. The Dwight Stable Value Fund is invested in the following:

•     A money market fund (TBC Pooled Employee Daily Liquidity Fund);

•     A fully benefit-responsive common/collective trust (the SEI Stable Asset Fund); and

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3. Fully Benefit-

    Responsive

    Investment

    Contracts

    Continued

•     Fully benefit-responsive synthetic guaranteed investment contracts (GICs) as follows:

a. Synthetic GIC, Dwight Managed Target 2, no specified maturity date, 5.20%;

b. Synthetic GIC, Dwight Managed Target 5, no specified maturity date, 5.20%;

c. Synthetic GIC, Dwight Managed Target 2, no specified maturity date, 5.19%;

d. Synthetic GIC, Dwight Managed Target 5, no specified maturity date, 5.19%

e. Synthetic GIC, Dwight Core International Fund, no specified maturity date, 5.20%; and

f.  Synthetic GIC, Dwight Core International Fund, no specified maturity date, 5.19%.

Synthetic GICs provide for a guaranteed return on principal over a specified period of time through fully benefit-responsive wrap contracts, issued by a third party, which are secured by underlying assets. The portfolio of assets underlying the synthetic GICs has a credit rating ranging from AA+ to AAA and includes diversified bond portfolios.

The wrap contracts are obligated to provide an interest rate not less than zero. These contracts typically provide that realized and unrealized gains and losses on the underlying assets are not reflected immediately in the net assets of the fund. Realized and unrealized gains and losses are amortized, usually over the time to maturity or the duration of the underlying investments, through adjustments to the future interest crediting rate.

The contract or crediting interest rates for the GICs are typically reset quarterly and are based on the market value of the portfolio of assets underlying these contracts. Inputs used to determine the crediting interest rates include each contract’s portfolio market value, current yield-to-date maturity, duration, and market value relative to contract value.

These wrap contracts provide benefit withdrawals and investment exchanges at the full contract value of the synthetic contracts (principal plus accrued interest) notwithstanding the actual market value of the underlying investments (fair value plus accrued interest).

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3. Fully Benefit-

    Responsive

    Investment

    Contracts

    Continued

Certain events may limit the ability of the Plan to transact at contract value with the issuer of fully benefit-responsive investment contracts. Such events include the following: (1) amendments to the Plan documents (including complete or partial plan termination or merger with another plan), (2) bankruptcy of the Plan sponsor or other Plan sponsor events (for example, divestitures or spin-offs of a subsidiary) that cause a significant withdrawal from the Plan, or (3) the failure of the trust to qualify for exemption from federal income taxes or any required prohibited transaction exemption under the ERISA, as amended. The Plan Administrator does not believe that the occurrence of any such event, which would limit the Plan’s ability to transact at contract value with participants, is probable.

The contracts provide that withdrawals associated with certain events which are not in the ordinary course of fund operations, and are determined by the issuer to have a material adverse effect on the issuer’s financial interest, may be paid at other than contract value.

Average duration for all investment contracts was 2.92 and 2.93 years at December 31, 2007 and 2006, respectively. Average yield data for all fully benefit-responsive investment contracts as of December 31, 2007 and 2006 was as follows:

4. Related Party

    Transactions

Certain Plan investments are managed by Putnam Investments, the Plan trustee, therefore, these transactions are exempt party-in-interest transactions. Transaction fees paid by the Plan for investment management services were included as a reduction of the return earned on each fund.

Transactions associated with Rio Tinto plc ADRs are considered exempt party-in-interest transactions because Rio Tinto plc is the Parent of the Company. As of December 31, 2007 and 2006, the Plan held 11,351 and 13,357 shares, respectively, of common stock of Rio Tinto plc, with a cost basis of $1,505,455 and $1,617,230, respectively. During the year ended December 31, 2007, the Plan recorded dividend income of $59,767 related to this stock.

11

4. Related Party

    Transactions

    Continued

At December 31, 2007 and 2006, the Plan held loans from participants totaling $2,704,260 and $2,611,022, respectively. Loans to participants, at cost, which approximates fair value, are at interest rates ranging from 5% to 10% and maturities ranging from 2008 to 2021.

5. Global

    Securities

    Lending

    Program

The Plan participates in the State Street Bank and Trust Company S&P 500 Flagship Securities Lending Series C Fund (the Fund), a common collective trust. The Fund invests in certain collective investment funds that participate in the Global Securities Lending Program maintained by State Street Bank. The State Street Bank and Trust Company Quality Funds for Short-Term Investment Super Collateral Fund and Quality D Short-Term Investment Fund (collectively referred to as “Cash Collateral Pools”) are cash collateral pools utilized by the underlying fund(s) for the investment of cash collateral resulting from securities lending activities.

The Cash Collateral Pools issue and redeem their units at a price of $1.00 per unit in accordance with their governing documents. Management of the Cash Collateral Pools monitors the variation between the per unit market value of each Pool’s portfolio and $1.00. Independent pricing services, quotations from bond dealers, and information with respect to bond and note transactions may be used to assist in determining market value; such pricing services may use valuation models or matrix pricing. Management of the funds has reviewed the basis on which management of the Cash Collateral Pools has determined to continue to issue and redeem units at a price of $1.00 per unit, including among other things current market conditions and the liquidity of the portfolio. Based on that review, Management of the funds has continued to fair value its holdings of units of each of the Cash Collateral Pools at $1.00 per unit. Management of the funds will continue to review the valuation of the units of the Cash Collateral Pools, including the basis for the valuation of those Pools by their management, and whether it continues to be appropriate to fair value the funds’ investment in those Pools at $1.00 per unit or, alternatively, at a lower per unit fair value.

12

6. Investments

The Plan’s investments, stated at fair value, that represent five percent or more of the Plan’s net assets available for benefits as of December 31, 2007 and 2006 are as follows:

During the year ended December 31, 2007, the Plan’s investments (including gains and losses on investments bought and sold, as well as held during the year) appreciated (depreciated) in value as follows:

7. Plan

    Termination

Although it has not expressed any intention to do so, the Company has the right under the Plan to discontinue its contributions at any time and to terminate the Plan subject to the provisions set forth in ERISA.

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8. Income Tax

    Status

The Internal Revenue Service has determined and informed the Company by a letter dated August 27, 2003, that the Plan and related trust were designed in accordance with the applicable requirements of the Internal Revenue Code. The Plan has been amended since receiving the determination letter; however, the Plan Administrator and the Plan’s legal counsel believe that the Plan is currently designed and being operated in compliance with the applicable requirements of the Internal Revenue Code. Therefore, no provision for income taxes has been included in the Plan’s financial statements.

9. Reconciliation of

    Financial

    Statements to

    Form 5500

The following is a reconciliation of net assets available for benefits as presented in the financial statements as of December 31, 2007 and 2006 to the Form 5500:

10. Delinquent

      Contributions

During the year ended December 31, 2007, Plan management determined that employee and Employer contributions totaling $231 for the payroll period ended March 30, 2007, had not been remitted to the Plan. As of December 31, 2007, the Company had not paid the delinquent contributions to the Plan. Plan management intends to remit $231 of contributions and related lost earnings of $197, which amounts were calculated under the guidelines of the U.S. Department of Labor’s Voluntary Fiduciary Correction Program (see the accompanying Supplemental Schedule of Delinquent Contributions).

11. Recent

      Accounting

      Pronouncements

In September 2006, the Financial Accounting Standards Board (“FASB”) issued Statement on Financial Accounting Standards No. 157 (“SFAS 157”), Fair Value Measurements. SFAS 157 establishes a single authoritative definition of fair value, sets out a framework for measuring fair value and requires additional disclosures about fair value measurement. SFAS 157 is effective for financial assets and liabilities for financial statements issued for fiscal years beginning after November 15, 2007 and for non-financial assets and liabilities for financial statements issued for fiscal years beginning after November 15, 2008. Plan management does not believe the adoption of SFAS 157 will have a material impact on the Plan’s financial statements.

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11. Recent

      Accounting

      Pronouncements

      Continued

In February 2007, the FASB issued Statement on Financial Accounting Standards No. 159 (SFAS 159), The Fair Value Option for Financial Assets and Financial Liabilities – including an amendment of FASB Statement No. 115. SFAS 159 provides an option to report selected financial assets and liabilities at fair value, which can be elected on an instrument-by-instrument basis. SFAS 159 is effective for financial statements issued for fiscal years beginning after November 15, 2007. Plan management does not believe the adoption of SFAS 159 will have a material impact on the Plan’s financial statements.

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Party in

Interest

Identity of Issue

Description of Investment

Money Market Fund:

Mellon Bank

TBC Pooled Employee Daily Liquidity Fund

Common/Collective Trusts:

SEI Investments

SEI Stable Asset Fund

State Street

State Street Bank and Trust Company S&P 500 Flagship Securities Lending Series C Fund

Total Common/Collective Trusts

Mutual Funds:

Dodge and Cox

Dodge and Cox Stock Fund

Harbor

Harbor Capital Appreciation Fund

Artisan

Artisan Mid Cap Fund

PIMCO

PIMCO Total Return Fund

*

Putnam

Putnam International Equity Fund

Dodge and Cox

Dodge and Cox International Fund

*

Putnam

Putnam Small Cap Growth Fund CL Y

UAM Trust Company

UAM/ICM Small Company Fund

Wells Fargo

Wells Fargo Advantage C&B Mid Cap Fund

Total Mutual Funds

See accompanying report of independent registered public accounting firm.

16

Party in
Interest

Identity of Issue

Description of Investment

Monumental Life Insurance Company

Synthetic GIC, Dwight Managed Target 2, no specified maturity date, 5.20%

Monumental Life Insurance Company

Synthetic GIC, Dwight Managed Target 5, no specified maturity date, 5.20%

Monumental Life Insurance Company

Synthetic GIC, Dwight Int Core Plus, no specified maturity date, 5.20%

State Street Bank

Synthetic GIC, Dwight Managed Target 2, no specified maturity date, 5.19%

State Street Bank

Synthetic GIC, Dwight Managed Target 5, no specified maturity date, 5.19%

State Street Bank

Synthetic GIC, Dwight Int Core Plus, no specified maturity date, 5.19%

Total Synthetic Guaranteed Investment Contracts

*

Rio Tinto plc ADRs

Common Stock

*

Various participants

Participant loans (maturing 2008 to 2021 at interest rates ranging from 5.0% to 10.0%)

*

Putnam

Pending Account

Total Investments

See accompanying report of independent registered public accounting firm.

17

Payroll

End

Date

Payroll

End

Date

Exhibit
Number

Document