For the last 200 years, these colorless and lustrous, pseudo cubes, of cryolite, from Greenland, a rare sodium, aluminum, fluoride, have been the standard for the species. The locality is not only now long gone, its underwater. THey mined it below sea level, to get cryolite as an important flux agent for the refining of alumninum. Associated with rust colored siderite, some of the cryolite crystals reach .7 cm across. This is a very showy, excellent, affordable, and good-sized example of this now-vanished species