Salammoniac

Sal ammoniac
Sal ammoniac from Tajikistan
General
Category	Halide mineral
Formula (repeating unit)	NH4Cl
Strunz classification	3.AA.25
Crystal system	Isometric
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Pm3m
Unit cell	a = 3.859 Å; Z = 1
Identification
Formula mass	53.49 g/mol
Color	Colorless, white, pale gray, may be pale yellow to brown if impure
Crystal habit	Crystals skeletal or dendritic; massive, encrustations
Twinning	On {111}
Cleavage	Imperfect on {111}
Fracture	Conchoidal
Tenacity	Sectile
Mohs scale hardness	1-2
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	1.535
Optical properties	Isotropic
Refractive index	n = 1.639
Birefringence	Weak after deformation
Ultraviolet fluorescence	no
Absorption spectra	no
Solubility	in water
References

Sal ammoniac is a rare mineral composed of ammonium chloride, NH₄Cl. It forms colorless, white, or yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and a brittle to conchoidal fracture. It is quite soft, with a Mohs hardness of 1.5 to 2, and it has a low specific gravity of 1.5. It is water-soluble. Sal ammoniac is also the archaic name for the chemical compound ammonium chloride. The Romans called the ammonium chloride deposits that they collected from near the Temple of Jupiter Amun (Greek Ἄμμων Ammon) in ancient Libya 'sal ammoniacus' (salt of Amun) because of proximity to the nearby temple. Salts of ammonia have been known from very early times; the term Hammoniacus sal appears in the writings of Pliny, but it is not known whether the term is identical with the more modern sal-ammoniac. In any case, that salt ultimately gave ammonia and ammonium compounds their name.

It typically forms as encrustations formed by sublimation around volcanic vents and is found around volcanic fumaroles, guano deposits and burning coal seams. Associated minerals include sodium alum, native sulfur and other fumarole minerals. Notable occurrences include Tajikistan; Mount Vesuvius, Italy; and Parícutin, Michoacan, Mexico.