A rare bottle-green gemstone, found only in the Moldau River valley in the Czech Republic (from which comes its name). Moldavite is a natural glass like obsidian. Though it was not discovered until the 18th century, it is believed to be one of the oldest gems on earth. Scientists don't agree on exactly how it formed; some think it was formed within the earth as a result of heat and pressure from meteorites, and some believe it is actually cooled material from those early meteorites. Because of these possible origins, moldavite is sometimes nicknamed "the stone of the heavens."