Shatner won a best supporting actor Emmy for Boston Legal last year

The 74-year-old actor agreed on Monday to sell the stone to GoldenPalace.com.

"This takes organ donors to a new height, to a new low, maybe. How much is a piece of me worth?" said Shatner.

The money will go to Habitat for Humanity. US TV show Boston Legal, in which Shatner stars, raised $20,000 (�11,317) for the charity last year.

Shatner, who played Captain Kirk on the original Star Trek TV series, passed the stone last autumn.

The actor was rushed to hospital after suffering "unbearable" backache that prompted him to drop to his knees in pain while filming on the set of Boston Legal, according to a TV interview last year.

"It was just unbelievable and it made you think about what pain is," he said.

This is a bold new addition to our fleet Richard Rowe, GoldenPalace.com

The operation is said to be excruciatingly painful, and the auction price includes the surgical stint and string used to permit passage of the stone.

The stone was so big, Shatner said, "you'd want to wear it on your finger".

"If you subjected it to extreme heat, it might turn out to be a diamond," he said.

Shatner persuaded doctors to return the stone last month, in order that he could offer it for auction.

GoldenPalace.com originally offered $15,000 (�8,500) for the kidney stone, but the actor turned it down, noting that his Star Trek tunics have sold for more than $100,000 (�56,634).

"This is a bold new addition to our fleet," GoldenPalace.com chief executive officer Richard Rowe said in a statement.

The website has a bizarre range of collectables, which includes a half-eaten toasted cheese sandwich said to bear the image of the Virgin Mary. It paid $28,000 for the item at auction