Crystal symmetry

Orthorhombic 2/m 2/m 2/m dipyramidal

Unit cell

Z = 8
a = 5.4558 Å
b = 9.1819 Å
c = 5.1429 Å

Formula mass

79.88 g^[1]

Color

Brown, yellowish brown, or black

Cristal habit

Tabular and striated, pyramidal or pseudohexagonal

Crystal system

Orthorhombic

Twinning

On {120}, uncertain

Cleavage

Poor on {120}, in traces on {001}

Mohs Scale hardness

5 1/2 to 6

Specific gravity

4.08 to 4.18

Optical properties

Biaxial (+)

Refractive index

n_α = 2.583
n_β = 2.584
n_γ = 2.700

Birefringence

∂   = 0.117

2V angle

Calculated: 12°  to 2°