Letovicite

Letovicite (/lɛtoʊˈvɪsaɪt/) is an ammonium sulfate mineral with composition (NH₄)₃H(SO₄)₂ (IUPAC: triammonium sulfate hydrogensulfate, Nickel–Strunz classification 07.AD.20).

Letovicite
White crystals of ammonium sulfate mineral letovicite from the Anna 2 Mine, Aachen, North Rhine – Westphalia, Germany.
General
Category	Sulfate mineral
Formula	(NH4)3H(SO4)2
IMA symbol	Let[1]
Strunz classification	07.AD.20
Dana classification	28.1.3.1
Crystal system	Monoclinic
Crystal class	Prismatic (2/m)
Space group	C2/c (no. 15)
Identification
Color	Colorless, white
Crystal habit	Tiny pseudo-hexagonal plates, granular
Twinning	Lamellar twinning
Cleavage	Distinct on {001}
Fracture	Uneven
Mohs scale hardness	1–2
Diaphaneity	Transparent
Specific gravity	1.83
Optical properties	Biaxial (−), colorless (transmitted light)
2V angle	75° (calc.)
Solubility	Soluble in water
References	[2]

It is a rare colorless or white monoclinic secondary mineral formed during the burning of waste coal heaps and as a deposit in hot springs. It was first described from the Letovice region of Moravia in 1932. Geologic occurrences also include Austria, Germany, Hungary, Italy, Poland, South Africa, Tajikistan and the United States.