An inscribed copy of Martin Luther King's memoir Stride Toward Freedom has sold for $49,335 at Hakes' Americana.
It beat an estimate of $35,000 by 40.9% in the July 16 sale.
The book is addressed to Chief Justice Earl Warren, the judge credited with helping overturn segregation in American schools in the landmark Brown v Board of Education ruling in 1954.
It's inscribed: "To Justice Earl Warren, In appreciation for your genuine good-will, your great humanitarian concern, and for your unswerving devotion to the sublime principles of our American democracy.
"With warm Regards, Martin L. King Jr."
Alex Winter, president of Hake's, comments: "The price paid for the book did not surprise us. It is a historic artifact of the highest magnitude and truly a one-of-a-kind piece.
"Both men associated with the book were integral figures in the Civil Rights Movement, and the importance of their legacy cannot be overstated.
"For this important work of literature to be signed by the author, Dr. King, to Chief Justice Warren places it in its own stratosphere when compared to other MLK Jr.-signed pieces, or any artifact associated with social consciousness, for that matter."
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