Clinohumite
| Clinohumite | |
|---|---|
| Chemical composition | Magnesium silicate |
| Hardness | 6 |
| Optic nature | Biaxial + |
| Refractive index | 1.628 - 1.674 |
| Birefringence | 0.024 - 0.041 |
| Specific gravity | ~ 3.21 |
| Lustre | Vitreous |
| Pleochroism | Strongly trichroic |
| Fluorescence |
SWUV: strong orange yellow |
Clinohumite is a member of the humite group. As a gemstone it is rare, but some cut stones are reported. The given below details are (largely) abstracted from Journal of Gemmology, 2007, 30, 5/6, 303-306 "A remarkably large clinohumite".
Contents
Crystallography
Monoclinic
Diagnostics
Color
Bright yellow-orange colour resembling some hessonite and spessartine garnets.
Cause of color: Mn
Diaphaneity
Transparent
Refractometer
Clinohumite has a biaxial optic character with a positive optic sign.
The refractive index range of clinohumite: nα = 1.628 - 1.638, nβ = 1.641 - 1.654, nγ = 1.662 - 1.674.
The maximum birefringence ranges from 0.024 to 0.041.
For a specific stone tested (9.45 ct. brownish orange clinohumite tested at the Gem Testing Laboratory, Jaipur): R.I.: 1.646-1.670, birefringence: 0.024.
Pleochroism
Strong trichroism: yellow, orange and brownish yellow.
Specific gravity
S.G.: ~ 3.21
Spectrum
Brownish-orange clinohumite.
General cut-off till 430nm (from 400nm).
Luminescence
SWUV: strong orange yellow;
LWUV: generally inert
Magnification
Inclusions: Strong color and growth zoning, flat paralles reflective planes, fluid like inclusions similar to trichites in tourmaline. Such liquid inclusions along with doubling appear very much like tourmaline; tube like inclusions; sometimes swirly zones.
Occurrence
Geographical 0ccurrence: Gem quality Clinohumite is known to occur in two important localities - The Pamir mountains (at Kukh-i-lal, Sumdzin and Changin); in Tajikistan in association with spinel and in the Taymyr region (Basin of Kotui river) in Siberia; Also in Mahenge, Tanzania.
References
- G.Choudhary and Chaman Golecha, A remarkably large Clinohumite, Journal of Gemmology, 2007, 30, 5/6, pp 303-306
- Henn, U., Hyrsl, J., and Milisenda, C.C., Gem Quality clinohumite from Tajikistan and the Taymyr region, Northern Siberia. Journal of Gemmology, 27(6), 335-9
- Hyrsl, J., 2001. Gem News International. Spinel with clinohumite from Mahenge, Tanzania, Gems and Gemology, 37(2), 144-5
- Laurs, B.M., and Quinn, E.P., 2004. Gem News International. Clinohumite from Mahenge, Tanzania. Gems and Gemology, 40(4), 337-8
- Gems Their Sources, Descriptions and Identification 4th Edition (1990) - Robert Webster (6th ed.)
- Colour Encyclopedia - J.E. Arem ISBN 0412989115
- Introduction to Optical Mineralogy 3rd edition (2003), Prof. W.D. Nesse
