← All gemstones
Corundum · Variety of Sapphire

Star Sapphire

Usually blue, gray, or black with asterism

Black Blue Gray
Optical properties

Optical characteristics

Ref. index
1.762 – 1.77
Birefringence
0.008 – 0.01
Luster
Vitreous
Pleochroism
Variable Variable; asterism may make pleochroism difficult to observe.
Fluorescence
Usually inert to variable.
Origins

Source localities

Myanmar Myanmar: Mogok Valley
Premium ★ Top Source

Classic source for ruby, sapphire, spinel and other collector gems.

37% est. supply
Sri Lanka Sri Lanka: Ratnapura / Elahera
Premium ★ Top Source

Classic Ceylon source for sapphire and many alluvial gems; known for bright colors and good clarity.

32% est. supply
India Kashmir: Zanskar Range
Legendary ★ Top Source

Kashmir star sapphires are exceedingly rare; the combination of Kashmir origin and asterism commands extreme premiums.

1% est. supply
Thailand Thailand: Chanthaburi / Kanchanaburi
Commercial

Historic ruby and sapphire area and major cutting/trading center; many stones are heat treated.

9% est. supply
Australia Australia: New South Wales / Queensland fields
Commercial

Commercial sapphire and opal source; many darker blue to blue-green sapphires.

6% est. supply
India India: Rajasthan / Odisha / Karnataka
Notable

Historic and modern source for garnet, moonstone, corundum and other gems.

15% est. supply
Treatments

Enhancement & treatment

Heat Heat Treatment, Corundum Heat is the most common corundum treatment. It can improve color and clarity, but… Diffusion Beryllium Diffusion Beryllium diffusion introduces light elements during high-temperature heating to alter body color. It must… Diffusion Surface Diffusion Surface diffusion adds coloring elements near the surface. It is less durable than body… Clarity Enhancement Flux Healing, Corundum Flux healing uses high temperature and flux to partially heal fractures in corundum. It… Clarity Enhancement Fracture Filling, Corundum Fracture filling improves apparent clarity in corundum. Lead-glass-filled ruby is the most important commercial…
Inclusions

Inclusions & features

Zoning Color Zoning Under 10x loupe in immersion: bands or patches of deeper or lighter color arranged… Crystals Crystal Inclusions Under 10x loupe: solid, well-formed mineral crystals trapped inside the host gem. They may… Synthetic Curved Growth Striae, Synthetic ID Under 10x loupe in immersion: curved parallel lines flowing through the stone in sweeping… Fractures Feathers and Fractures Under 10x loupe: irregular internal surfaces that catch light and appear bright, wing-like, or… Fractures Fingerprint Inclusions Under 10x loupe: curved or wavy lines of tiny dots forming patterns that look… Crystals Negative Crystals Under 10x loupe: an empty cavity that has the geometric shape of the host… Clouds Pinpoint Clouds Under 10x loupe: concentrations of extremely tiny bright dots that individually are too small… Needles Silk, Rutile Needles Under 10x loupe: extremely fine bright lines crossing in three directions at 60° angles.… Multiphase Two-Phase Inclusions Under 10x loupe: a transparent irregular cavity containing both a liquid phase and a…
Identification

Instruments used

Dichroscope Reveals pleochroism, instantly eliminates singly-refractive stones Immersion Microscope See every internal detail clearly, the professional standard 10x Loupe Your most-used instrument, start every examination here Polariscope Determines single vs. double refraction, quick and conclusive Refractometer Measures refractive index, the backbone of gem identification UV Lamp, Long Wave and Short Wave Fluorescence exposes treatments, synthetics, and origin