Selenite Tower

Selenite, satin spar, desert rose, gypsum flower are crystal habit varieties of the mineral gypsum. All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate, with the chemical formula CaSO₄·2H₂O. 

Hardness: 2 gem-a.com

Color: Brown green, brownish yellow, greenish, gray green, gray white

Cleavage: Perfect,, Distinct,, Distinct

Streak: White

Luster: Pearly

Fracture: Fibrous – thin, elongated fractures produced by crystal forms or intersecting cleavages (e.g. asbestos)

Optical properties: Biaxial (-) 2V=58

Sodium selenite (Na2SeO3) is a toxic inorganic salt that is highly soluble in water and insoluble in organic solvents. The crystal structure of the anhydrous salt has been variously reported as tetragonal or monoclinic.

Some of the largest crystals ever found are of selenite, the largest specimen found in the Naica Mine's Cave of the Crystals being 55tons!