Tungstite

Tungstite is a hydrous tungsten oxide mineral with formula: WO₃·H₂O. It is a secondary mineral formed by the weathering of other tungsten containing minerals. It crystallizes in the orthorhombic system in translucent yellow to yellow green masses. It is clay-like with Mohs hardness of 2.5 and a specific gravity of 5.5.

Tungstite
Bright yellow tungstite on ferberite
General
Category	Minerals
Formula	WO3·H2O
IMA symbol	Tgs[1]
Strunz classification	4.FJ.10
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pmnb
Identification
Formula mass	249.86 g/mol
Color	Yellow, yellowish green/orange
Crystal habit	Earthy, pulverulent
Cleavage	Perfect along [001], imperfect along [110]
Mohs scale hardness	2.5
Luster	Resinous, pearly
Streak	Yellow
Diaphaneity	Transparent
Specific gravity	5.517
Optical properties	Biaxial (-)
Refractive index	nα = 2.090, nβ = 2.240, nγ = 2.260
Birefringence	δ = 0.170
Dispersion	r < v (strong)

It was first described in 1868 for an occurrence near Trumbull, Connecticut at the Hubbard Tungsten Mine at Long Hill.