Star Garnet
Last updated: April 2026
Star garnet is the asteriated variety of almandine, displaying a 4-rayed star from two sets of rutile and/or hematite needle inclusions at right angles — the key distinction from star corundum's 6-rayed star. Idaho star garnets occasionally produce a rare 6-rayed star. Star is visible only under a single directional point light. Sources: Idaho (USA) and Rajasthan (India). No commercial synthetic.
Physical & Optical Properties
RI Range1.770–1.830
SG Range3.93–4.30
SG Typical4.05
Hardness (Mohs)7–7.5
Crystal SystemCubic
Optic CharacterSR (Singly Refractive)
Dispersion0.024
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsRed Pink, Purple, Brown
SpeciesGarnet
VarietyStar Almandine
Related: Garnet Varieties
Key Differentiators
- 4-rayed star (occasionally 6-rayed in Idaho material) visible under a direct point light source
- Isotropic SR — 4 rays vs the 6-rayed star typical of corundum (star ruby/sapphire)
- Inert under UV fluorescence (star ruby shows strong red LW)
- Chelsea filter inert (star ruby reacts red)
- Almandite trio absorption spectrum (~504, 520, 573 nm)
- Strong magnetism from high iron content
Common Simulants
- Star Ruby: Star ruby is doubly refractive (DR_U-), shows strong red LW fluorescence, Chelsea filter strongly red, and typically displays a 6-rayed star. RI 1.762–1.778 vs star garnet 1.77–1.83 (higher). RI separates these reliably.
- Star Sapphire: Star sapphire is doubly refractive, blue/grey/pink body color. 6-rayed star. Inert to weak LW fluorescence. RI 1.762–1.778. Refractometer and body color distinguish easily.
- Glass with foil star: Glass is isotropic with a low SG (typically 2.3–4.5) and much lower RI (~1.50–1.70). The star in glass is a surface reflection from a foil backing — visible as a flat metallic layer under magnification — not internal asterism.
Commonly Confused With
Commonly confused with: Star Ruby.
Price Context
Natural — low ($/ct)$5
Natural — high ($/ct)$200
NotePer carat; most Idaho/Indian star garnets are –/ct; fine Idaho stones with rare 6-rayed star reach –/ct
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a star garnet? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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