Chloritoid
Mineral (Fe,Mg,Mn)2Al4Si2O10(OH)4
Also called Ottrelite
About it
Dark grey-green brittle plates in schist and phyllite; much harder than chlorite and its flakes snap rather than bend. Common in aluminium-rich metamorphic rocks.
- Type
- Mineral
- Group
- Silicate (nesosilicate), chloritoid group
- Formula
- (Fe,Mg,Mn)2Al4Si2O10(OH)4
- Hardness (Mohs)
- 6.5
- Specific gravity
- 3.46–3.8
- Streak
- white to greenish grey
- Lustre
- pearly, vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- dark grey, greenish grey, greenish black
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- perfect in one direction, brittle flakes
Typical values: real specimens vary. For more, see mindat.org.