Voltaite
Mineral K2Fe2+5Fe3+3Al(SO4)12·18H2O
Take care.
- Damaged by water: Keep it dry: don't wash it, and keep it out of damp places.
About it
Black, glassy cubes and octahedrons of a soluble iron sulfate, formed as pyrite oxidizes in mines and at volcanic vents. Named for Alessandro Volta and first found at the Solfatara near Naples.
- Type
- Mineral
- Group
- Sulfate, voltaite group
- Formula
- K2Fe2+5Fe3+3Al(SO4)12·18H2O
- Hardness (Mohs)
- 3
- Specific gravity
- 2.7–2.8
- Streak
- greyish green
- Lustre
- resinous, vitreous (glassy)
- Crystal system
- Isometric (cubic)
- Colours
- black, greenish black, dark green, brown
- Transparency
- opaque, translucent
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.