A rare rock from Mars known as Meteorite NWA 16788 will be up for auction at Sotheby's on July 16. The meteorite may sell for as much as $4 million, according to the auction house.

Ejected material, mostly breccia (angular rocks cemented by clay), can be found far as 3 to 4 km (1.8 to 2.5 mi) from the largest craters.” ...