Clinohumite
Last updated: April 2026
Clinohumite is a rare magnesium iron silicate of the humite group, only occasionally faceted as a gemstone. Yellow-orange clinohumite from Tajikistan (Pamirs) and from Mahenge, Tanzania, constitutes most gem-quality material. Its yellow-orange color and high SG cause frequent confusion with spessartite garnet, but the biaxial doubly refractive character of clinohumite is immediately distinguishable from spessartine's isotropic singly refractive character under a polariscope.
Clinohumite has a specific gravity of 3.21 and a refractive index of 1.625–1.675, with a Mohs hardness of 6. It is biaxial +.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Key Differentiators
- Biaxial DR (monoclinic) — shows 4 extinction positions per rotation under polariscope; spessartine is isotropic SR
- RI 1.625–1.675 with moderate facet doubling (birefringence 0.028)
- SG 3.13–3.35 — overlaps spessartite range (3.57–3.83) but significantly lower
- Weak pleochroism (yellow / pale yellow / orange-yellow) — spessartine is isotropic and shows none
- Rare collector gem; most material from Tajikistan or Tanzania
Commonly Confused With
Commonly confused with: Spessartite Garnet, Hessonite Garnet.
Measurement Guides
Identifying a clinohumite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Clinohumite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →