Clinohumite

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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
LWUV: generally inert

A 9.45 ct brownish orange clinohumite tested at the Gem Testing Laboratory, Jaipur.


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.

Crystallography

Monoclinic

Diagnostics

Color

Bright yellow-orange colour resembling some hessonite and spessartine garnets.
Cause of color: Mn

Diaphaneity

Transparent

Refractometer

R.I. variable 1.646-1.670 for a specific stone tested (9.45 ct. brownish orange clinohumite tested at the Gem Testing Laboratory, Jaipur).
D.R.: 0.024 Anisotropic, biaxial positive.

Pleochroism

Strong trichroism: yellow, orange and brownish yellow.

Specific gravity

S.G.: 3.21

Spectrum

Diffraction spectrum

Orange-brown clinohumite.
General cut-off till 430nm (from 400nm).


Luminescence

SWUV: strong orange yellow;
LWUV: generally inert

Magnification

Inclusions: Strong colour 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.

References

  • G.Choudhary and Chaman Golecha, A remarkably large Clinohumite, Journal of Gemmology, 2007, 30, 5/6, pp 303-306
  • Colour Encyclopedia of Gemstones by J.E.Arem
  • 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 by Webster.