probably from Caverna de Santo Domingo near Santa Eulalia, Chihuahua, Mexico
Unknown, but younger than the Early Cretaceous limestone making up the cave in which the crystals were found.
These five, clear-to-translucent, sword-like selenite crystals range in lenght from 122 to 160 centimeters (4 to 4.25 feet). They were first believed to have been taken from the 100 meter-long room of the "Cave of Swords" section of the Gibralter Silver Mine near Nacia, Chihuahua, Mexico. Current belief is that they were removed from one of the "rooms" of the Caverna de Santo Domingo, located near Santa Eulalia, Chihuahua, Mexico. Both mines are situated in the 97 million year old limestones from which sulfide-ore minerals have been extracted. The selenite (CaSO4*2H2O) crystals were created as water migrated through the ore-rich, Early Cretaceous limestones, dissolving the sulfide ores and prodicing sulfuric acid. As water reacted with the limestone, it became saturated with calcium and sulfate resulting in the gypsum being precipitated out of solution to form the large clear to colorless selenite crystals.