Mascagnite

Mascagnite is a rare ammonium sulfate mineral (NH₄)₂SO₄. It crystallizes in the orthorhombic system typically forming as stalactitic masses exhibiting good cleavage. It is soft (not higher than 2.5 on the Mohs scale) and water-soluble. Optical properties are variable; the purest form is transparent and colorless, but opaque gray or yellow deposits are also known.

Mascagnite
Acicular crystals and flakes of Mascagnite
General
Category	Sulfate mineral
Formula	(NH4)2SO4
IMA symbol	Msc[1]
Strunz classification	7.AD.05
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnam
Identification
Color	Colorless, grey, yellowish-grey, yellow
Cleavage	Distinct/ good On {001}
Fracture	Irregular/ uneven
Tenacity	Sectile
Mohs scale hardness	2 – 2+1⁄2
Luster	Vitreous, dull
Diaphaneity	Transparent, translucent, opaque
Density	1.768 g/cm3
References	[2][3][4][5]

It occurs in fumaroles, as at Mount Vesuvius and associated with coal seam fires. It was named for Italian anatomist Paolo Mascagni (1752–1815) who first described the mineral.