Annite
Mineral KFe3AlSi3O10(OH)2
Take care.
- Fragile: Handle it gently and pack it well; it breaks or crumbles easily.
About it
The iron-rich end of the biotite series: black mica in granite and pegmatite, as at Cape Ann, Massachusetts, Pikes Peak, Colorado, and Mont Saint-Hilaire, Quebec.
- Type
- Mineral
- Group
- Silicate (phyllosilicate), mica group
- Formula
- KFe3AlSi3O10(OH)2
- Hardness (Mohs)
- 2.5–3
- Specific gravity
- 3.3
- Streak
- white to grey
- Lustre
- vitreous (glassy), pearly
- Crystal system
- Monoclinic
- Colours
- black, dark brown
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- perfect in one direction, flexible elastic sheets
Typical values: real specimens vary. For more, see mindat.org.