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.
Star Garnet has a specific gravity of 4.05 and a refractive index of 1.770–1.830, with a Mohs hardness of 7.0–7.5. It is singly refractive.
Physical & Optical Properties
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
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.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Star Garnet is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
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