Cummingtonite
Mineral (Mg,Fe)7Si8O22(OH)2
Take care.
- Can shed asbestos fibres: Keep it in a closed box, and never break, saw, sand, or scrape it.
About it
Beige to brown fibrous or radiating amphibole of metamorphic rocks, the magnesium-rich partner of grunerite; named for Cummington, Massachusetts. Fibrous forms count as asbestos.
- Type
- Mineral
- Group
- Silicate (inosilicate), amphibole group
- Formula
- (Mg,Fe)7Si8O22(OH)2
- Hardness (Mohs)
- 5–6
- Specific gravity
- 3.1–3.3
- Streak
- white
- Lustre
- silky, vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- beige, brown, grey, pale green
- Transparency
- transparent, translucent
- Cleavage and fracture
- good in two directions at about 56° and 124°
Typical values: real specimens vary. For more, see mindat.org.