Halotrichite
Mineral Fe2+Al2(SO4)4·22H2O
Also called Feather alum and Iron alum
Take care.
- Damaged by water: Keep it dry: don't wash it, and keep it out of damp places.
- Breaks down in damp air: Keep it dry and in steady humidity; some crumble or rot as they take on moisture.
- Fragile: Handle it gently and pack it well; it breaks or crumbles easily.
About it
Hair-like white fibres and silky tufts formed where pyrite weathers in shale and coal. Very soluble, and the fibres crush easily; the magnesium-rich pickeringite looks the same.
- Type
- Mineral
- Group
- Sulfate, halotrichite group
- Formula
- Fe2+Al2(SO4)4·22H2O
- Hardness (Mohs)
- 1.5–2
- Specific gravity
- 1.89–1.95
- Streak
- white
- Lustre
- silky, vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- white, colourless, yellowish, greenish
- Transparency
- transparent, translucent
- Cleavage and fracture
- no useful cleavage; grows in hair-like fibres
Typical values: real specimens vary. For more, see mindat.org.