Stilpnomelane
Mineral K(Fe,Mg)8(Si,Al)12(O,OH)27
About it
Black to bronze mica-like plates and sprays that snap rather than bend; common in banded iron formations such as Western Australia's Hamersley Ranges.
- Type
- Mineral
- Group
- Silicate (phyllosilicate), stilpnomelane group
- Formula
- K(Fe,Mg)8(Si,Al)12(O,OH)27
- Hardness (Mohs)
- 3–4
- Specific gravity
- 2.59–2.96
- Streak
- white to grey
- Lustre
- pearly, vitreous (glassy), submetallic
- Crystal system
- Triclinic
- Colours
- black, greenish black, bronze
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- perfect in one direction, brittle flakes
Typical values: real specimens vary. For more, see mindat.org.