Crystal Nuummite

Category

Mineral variety

Formula
(repeating unit)

(Mg
2)(Mg
5)Si
8O
22(OH)
2

Identification

Formula mass

780.82 gm

Color

Black, grey

Twinning

None

Cleavage

Perfect on 210

Fracture

Conchoidal

Mohs scalehardness

5.5 - 6.0

Luster

Vitreous/glossy

Diaphaneity

opaque

Density

2.85 - 3.57

Refractive index

1.598 - 1.697 Biaxial

Birefringence

0.0170 - 0.230