Silicates — humite group · Sourced PROFILE
Clinohumite
(Mg,Fe²⁺)₉(SiO₄)₄(F,OH)₂
A magnesium-rich humite-group mineral whose yellow to orange crystals are documented at Kuh-i-Lal in the South Pamir.
AT A GLANCE
- Formula
- (Mg,Fe²⁺)₉(SiO₄)₄(F,OH)₂
- Crystal system
- Monoclinic
- Space group
- P2₁/c
- Mohs hardness
- 6
- Density
- 3.17–3.35 g/cm³
- Optical character
- Biaxial (+), strongly dispersive
CRYSTALLOGRAPHY
Crystal form & structure
Complex, highly modified crystals to about 2 cm; also massive. Simple and lamellar twinning on {100} is common.
HAND-SAMPLE PROPERTIES
Physical properties
- Cleavage
- Poor on {100}
- Fracture
- Uneven to subconchoidal
- Tenacity
- Brittle
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Observed colours
- White, yellow to brown; pale yellow to golden yellow in thin section
LIGHT & OPTICS
Optical properties
- Optical class
- Biaxial (+), strongly dispersive
- Refractive index
- nα 1.628–1.638; nβ 1.641–1.654; nγ 1.662–1.674
- Fluorescence & electrical behaviour
- No diagnostic fluorescence is reported in the cited profile.
GEOLOGICAL SETTING
Formation
Forms in contact-metamorphosed dolostone and metasomatized limestone, and in some ultramafic or carbonatite settings.
MINERAL COMPANY
Common associations
Grossular, wollastonite, forsterite, monticellite, dolomite, calcite, talc, biotite, spinel and vesuvianite
FIELD NOTES
How to identify it
Hardness 6, yellow-orange colour, poor cleavage and association with magnesium-rich marble minerals are suggestive; optical or chemical analysis separates it from similarly coloured silicates.
NAME & HISTORY
Where the name comes from
The name combines its monoclinic crystal system with its relationship to humite.
SCIENTIFIC SOURCE
Handbook of Mineralogy — Clinohumite
External reference; factual profile paraphrased and attributed. Copyright remains with the publisher.
PROVENANCE
Documented occurrences
Kuh-i-Lal district, Ishkoshim · Clinohumite occurs with sapphirine and other minerals in an ultra-magnesian metamorphic lens at Kuh-i-Lal. This record exposes district context only, not collecting coordinates.
Sourced · District precisionSapphirine + Forsterite and Sapphirine + Humite-Group Minerals in an Ultra-Magnesian Lens from Kuhi-lal, SW Pamirs, Tajikistan