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Acicular crystals and flakes of Mascagnite
Category Sulfate mineral
(repeating unit)
Strunz classification 7.AD.05
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnam
Color Colorless, grey, yellowish-grey, yellow
Cleavage Distinct/ good
On {001}
Fracture Irregular/ uneven
Tenacity Sectile
Mohs scale hardness 2 - ​2 12
Luster Vitreous, dull
Diaphaneity Transparent, translucent, opaque
Density 1.768 g/cm3
References [1][2][3][4]

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.

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.