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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

RI Range1.625–1.675
SG Range3.13–3.35
SG Typical3.21
Hardness (Mohs)6
Crystal SystemMonoclinic
Optic CharacterDR Biaxial (+)
Birefringence0.028
Dispersion0.022
Fluorescence LWInert
Fluorescence SWStrong orange
Chelsea FilterInert
PleochroismWeak
ColorsYellow Orange, Brown
SpeciesClinohumite (Mg,Fe)₉(SiO₄)₄(F,OH)₂
Yellow OrangeBrown

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

Clinohumite varies 1.625 – 1.675 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORotate the stone through a full 360°, reading both edges atevery 45°. SEETwo boundaries, 0.028 apart at their widest separation. Thepair drawn here is one specimen: this species is publishedat 1.625 – 1.675, and the two edges slide together anywhereacross it, between the dashed marks. MEANSThat gap IS the birefringence — and it is the stable part.Where the pair sits varies by 2 printed divisions from stoneto stone, so the gap identifies and the position onlynarrows. Take max minus min across the whole rotation; asingle position understates it. Computed from gems.json — edge positions are arithmetic, not drawn. RI increases upward; the field above the boundary is the dark one.

Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.

Through the polariscope

Clinohumite Blinks 4× per turn (DR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Clinohumite blinks light-dark four times in a full turn. That is doubly refractive. It does NOT tell you uniaxial from biaxial — that is the optic figure, which needs a conoscope. Computed from optic character and transparency in gems.json. A polariscope separates singly refractive, doubly refractive and aggregate — it does not show the optic sign.

Drawn from the optic character and transparency above. A polariscope separates singly refractive, doubly refractive and aggregate; the optic sign needs a conoscope. How to take this reading.

Specific gravity, and what it rules out

Clinohumite SG 3.13–3.35 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 17 other species in the table overlap this range, so a reading here narrows the field to 18 rather than naming the stone. Combine it with a refractive index to separate what is left. Computed from the specific-gravity range in gems.json. Hydrostatic weighing — the bench method this site recommends; heavy liquids are toxic and regulated. Faint ticks are the other species in the table.

Drawn from the specific-gravity range above, against every other species in the table. How to take this reading.

Through the dichroscope

Clinohumite Trichroic — two of three at a time BEST ORIENTATION ROTATED 45° — THE NULL At its best orientation Clinohumite shows yellow in one window and pale yellow in the other. Rotate the instrument 45° and the two windows become IDENTICAL — the null. So "both windows the same" means either the stone is singly refractive or you are holding the instrument at the wrong angle, and the only way to tell is to turn it. Clinohumite is trichroic: a third colour, orange-yellow, appears in a different orientation, and a dichroscope only ever shows two at once. Computed from pleochroism and pleochroic colours in gems.json. Window tints are derived mechanically from the colour words, not chosen; a neutral pair depicts no colour at all.

Drawn from the pleochroism above. Two windows that match mean either no pleochroism or the wrong angle — turn the instrument to tell. How the dichroscope compares.

Key Differentiators

Commonly Confused With

Commonly confused with: Spessartite Garnet, Hessonite Garnet.

Measurement Guides

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing

Identifying a clinohumite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.

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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.

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