Pickeringite
Mineral MgAl2(SO4)4·22H2O
Also called Magnesia 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
Silky white fibres and crusts in weathered shale, coal beds, and mine walls, the magnesium partner of halotrichite. Tests are needed to tell the two apart; dissolves in water.
- Type
- Mineral
- Group
- Sulfate, halotrichite group
- Formula
- MgAl2(SO4)4·22H2O
- Hardness (Mohs)
- 1.5–2
- Specific gravity
- 1.73–1.79
- Streak
- white
- Lustre
- silky, vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- white, colourless, yellowish, pinkish
- Transparency
- transparent, translucent
- Cleavage and fracture
- no useful cleavage; grows in hair-like fibres
Typical values: real specimens vary. For more, see mindat.org.