Star Sapphire

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Physical & Optical Properties

RI Range1.762–1.770

SG Range3.95–4.03

SG Typical4.00

Hardness (Mohs)9

Crystal SystemTrigonal

Optic CharacterDR Uniaxial (−)

Birefringence0.008

Dispersion0.018

Fluorescence LWVariable

Fluorescence SWInert

Chelsea FilterInert

PleochroismStrong Dichroic

ColorsBlue Violet, Black, Colorless, Purple, Red Pink, Yellow Orange

SpeciesCorundum

Key Differentiators

6-rayed star under point light source (asterism)
Caused by intersecting rutile silk needles at 60°/120°
Hardness 9
Inert to Chelsea filter (unlike some blue simulants)

Natural vs. Synthetic

Synthetic star sapphire is commercially available (Flame fusion / Linde process (most common synthetic star sapphire)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

GemID Pro includes a two-phase natural vs. synthetic testing protocol for Star Sapphire.

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Common Simulants

Star spinel: Isotropic SR; 4-rayed star; no trichroism; RI ~1.718; different UV fluorescence.
Glass with foil: Isotropic; star is surface reflection from foil, not internal; look for foil layer edge at girdle.
Synthetic star spinel: Isotropic; 4-rayed star; RI ~1.727; anomalous DR under polariscope; Chelsea filter variable.

Commonly Confused With

Commonly confused with: Spinel, glass, synthetic spinel, Star Diopside.

Treatments

Heat Treatment
Beryllium Diffusion (color change)
Surface Coating (star or color enhancement)

Price Context

Natural — low ($/ct)$50

Natural — high ($/ct)$15,000

NotePer carat; blue star sapphires with sharp 6-ray star and good color can reach $1,000–$15,000/ct (Burma/Ceylon); black star sapphires are common at $50–$200/ct

Synthetic — low ($/ct)$5

Synthetic — high ($/ct)$40

Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.

About Star Sapphire

Star sapphire displays a 6-rayed star from three sets of rutile silk inclusions. Blue and grey-blue are the most common colors; black star sapphire (Thailand, Cambodia) is the most affordable. Sources include Sri Lanka and Myanmar. Linde synthetic star sapphires (Verneuil process) are common in vintage jewelry — very sharp centered star and chalky blue LW fluorescence. Heat treatment destroys silk needles, so fine natural star sapphires are sold unheated.

Identifying a star sapphire? GemID walks through these tests in order — RI, SG, fluorescence, and more.

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