Selenite

Selenite is a transparent and colorless variety of the mineral gypsum. It is known for being so soft that it can be scratched with a fingernail. It has three unequal cleavages and is typically formed by evaporation of salt waters. It has been found in crystals over 40 feet long in localities in Mexico. Selenite is found in areas of Mexico and the U.S. in clusters of crystals resembling rosettes, popularly known as desert roses.