Sign warning visitors not to remove trinitite from Trinity Site, New Mexico, USA. This was the site of the Trinity Test, the first ever nuclear explosion, on the 16th of July 1945, as part of the Manhattan Project. This explosion created trinitite, an altered silicate resembling rough green glass. The extreme temperatures of the nuclear explosion melted the native sandstone soil. As the material cooled it formed a glassy structure. The greenish colour comes from iron in the sand. Twice a year Trinity Site opens to the public, and though trinitite can still be found there, its removal is prohibited by the US army.