Colony Financial Inc. shares fell more than 6 percent Thursday after the real estate investment trust announced a secondary offering of nearly 12.4 million shares.

The Santa Monica REIT, which specializes in commercial mortgages, said it will offer 11.6 million of the shares, with net proceeds to be used for acquisitions. If sold at Thursday’s closing price, that share of the offering will result in gross proceeds of about $218 million.

Selling shareholders of another 750,000 shares include Cedar Bridge Institutional Fund LP and Cedar Bridge Realty Fund LP, which are selling stakes of 1.7 percent and 2.6 percent respectively. The underwriters, which include BofA Merrill Lynch, Goldman, Sachs & Co., Morgan Stanley and UBS Investment Bank, have the option to purchase up to an additional 1.85 million shares to cover any overallotments.

Colony Financial, which went public in September 2009, is a subsidiary of billionaire Thomas J. Barrack Jr.’s Colony Capital LLC. Colony Financial has about 17.4 million shares outstanding.

Shares closed down $1.34, or 6.6 percent, to $18.83 on the New York Stock Exchange.