Wulfenite

Wulfenite
Wulfenite from Red Cloud mine, Arizona
General
Category	Molybdate mineral
Formula (repeating unit)	PbMoO4
IMA symbol	Wul[1]
Strunz classification	7.GA.05
Crystal system	Tetragonal
Crystal class	Dipyramidal (4/m) H-M symbol: (4/m)
Space group	I41/a
Unit cell	a = 5.433, c = 12.110 [Å]; Z = 4
Identification
Color	Orange-yellow, yellow, honey-yellow, reddish-orange, rarely colorless, grey, brown, olive-green and even black
Crystal habit	Thin tabular to pyramidal
Twinning	Twins on the [001] common
Cleavage	On {011}, distinct; on {001}, {013}, indistinct
Fracture	Irregular to sub-conchoidal
Tenacity	Brittle
Mohs scale hardness	3
Luster	Adamantine, resinous
Streak	White
Diaphaneity	Transparent to opaque
Specific gravity	6.5–7.0
Optical properties	Uniaxial (−), may be anomalously biaxial
Refractive index	nω = 2.405 nε = 2.283
Birefringence	δ = 0.122
Pleochroism	Weak; orange and yellow
Ultraviolet fluorescence	None
Other characteristics	Specimens may be piezoelectric
References	[2][3][4]

Wulfenite is a lead molybdate mineral with the formula PbMoO₄. It often occurs as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called "yellow lead ore".

It crystallizes in the tetragonal system, often occurring as stubby, pyramidal or tabular crystals. It also occurs as earthy, granular masses. It is found in many localities, associated with lead ores as a secondary mineral associated with the oxidized zone of lead deposits. It is also a secondary ore of molybdenum, and is sought by collectors.