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Demantoid Garnet

Last updated: April 2026

The green variety of andradite garnet, prized for its exceptional brilliance and fire. "Horsetail" inclusions (chrysotile fibers radiating from a chromite crystal) are diagnostic for Russian (Ural) demantoid but absent in Namibian material. Horsetails confirm andradite species but not the demantoid variety — color and RI confirmation are still required.

Demantoid Garnet has a specific gravity of 3.84 and a refractive index of 1.880–1.895, with a Mohs hardness of 6.5–7.0. It is singly refractive.

Physical & Optical Properties

RI Range1.880–1.895
SG Range3.82–3.88
SG Typical3.84
Hardness (Mohs)6.5–7
Crystal SystemCubic
Optic CharacterSR (Singly Refractive)
Dispersion0.057
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterRed
PleochroismNone
ColorsGreen, Yellow Orange
SpeciesGarnet
VarietyDemantoid
GreenYellow Orange

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

Demantoid Garnet no reading — over the limit 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORead the scale from bottom to top, then look for theliquid’s own faint line near the top. SEEThe field stays dark, with one faint line near 1.81 thatdoes not move when you change stones. MEANSOver the limit — this stone’s index is above the contactliquid’s own, so the liquid is the last thing the instrumentcan still see. That faint line is your proof the instrumentis working rather than dead. It is a RESULT: it eliminatesevery species below 1.81 in one observation. A field darkwith NO line means something else has gone wrong. 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

Demantoid Garnet Dark throughout (SR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Demantoid Garnet stays dark through the whole rotation. That is singly refractive: there is no second ray to rotate the plane of vibration back into the analyser. 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

Demantoid Garnet SG 3.82–3.88 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 4 other species in the table overlap this range, so a reading here narrows the field to 5 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

Demantoid Garnet One colour (no pleochroism) IDENTICAL AT EVERY ANGLE Demantoid Garnet shows no pleochroism, so both windows match at every orientation — turning the instrument changes nothing. That is a real negative result, and the reason it is worth knowing is below. 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.

Almandine GarnetColor-Change GarnetHessonite GarnetPyrope GarnetRhodolite GarnetSpessartite GarnetStar GarnetTsavorite Garnet

Key Differentiators

Common Simulants

Commonly Confused With

Commonly confused with: Tsavorite Garnet, Peridot, Zircon, Glass.

Treatments

Measurement Guides

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

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

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Studying for the GIA, FGA, or FEEG practical? Demantoid Garnet 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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