Star Diopside
Black asteriated diopside from India displaying a 4-rayed star from two sets of magnetite and ilmenite needle inclusions oriented perpendicular in the (010) plane. The 4-rayed star distinguishes it from star corundum (6-rayed).
Physical & Optical Properties
RI Range1.664–1.721
SG Range3.27–3.36
SG Typical3.29
Hardness (Mohs)5–6
Crystal SystemMonoclinic
Optic CharacterDR Biaxial (−)
Birefringence0.030
Dispersion0.013
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsBlack
SpeciesDiopside
VarietyBlack Star Diopside
Key Differentiators
- 4-rayed star (not 6-rayed) — caused by two sets of magnetite/ilmenite needles perpendicular in (010) plane
- Black to dark greenish-black opaque body color
- Lower hardness than star corundum (5.0–6.0 vs 9.0) — easily scratched
- Strong magnetic response from magnetite needle inclusions
- India origin (Karnataka, Tamil Nadu) — essentially the only commercial source
Common Simulants
- Black Star Sapphire: Star sapphire is corundum (hardness 9, vs diopside 5–6). RI 1.762–1.778 vs diopside 1.664–1.721. Star sapphire typically shows 6 rays; star diopside shows 4 rays. Star sapphire is non-magnetic; star diopside shows weak magnetism from magnetite inclusions. SG 3.99–4.05 vs diopside 3.27–3.36.
- Black Star Spinel: Star spinel shows a 4-rayed star like diopside but is isotropic (SR, cubic) with single RI near 1.718. Diopside is biaxial (DR_B+) showing a birefringence spread of 0.030 on the refractometer. SG spinel 3.58–3.61 vs diopside 3.27–3.36.
- Glass with foil star: Glass is isotropic, much lower SG (typically 2.3–4.5), and the star is a surface reflection from a foil backing rather than internal asterism from needle inclusions. Under magnification the foil layer is visible at the base.
Commonly Confused With
Commonly confused with: Star Ruby, Star Sapphire.
Price Context
Natural — low ($/ct)$5
Natural — high ($/ct)$50
NotePer carat; low-value ornamental gem; $5–20/ct for commercial grade; $20–50/ct for clean, well-cut stones with sharp bright star
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
About Star Diopside
Black asteriated diopside from India displaying a 4-rayed star from two sets of magnetite and ilmenite needle inclusions oriented perpendicular in the (010) plane. The 4-rayed star distinguishes it from star corundum (6-rayed).
Identifying a star diopside? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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