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Corundum

Sapphire

All corundum colors except ruby red, including blue, pink, yellow, green, purple and colorless.

Black Blue Color Change Colorless Gray Green Orange Pink Purple White Yellow
Optical properties

Optical characteristics

Ref. index
1.762 – 1.77
Birefringence
0.008 – 0.01
Luster
Vitreous
Pleochroism
Moderate to strong Usually distinct; colors depend on body color.
Fluorescence
Usually inert to variable; some fancy sapphires fluoresce.
Origins

Source localities

Sri Lanka Sri Lanka: Ratnapura / Elahera
Premium ★ Top Source

Classic Ceylon quality; vivid cornflower to royal blue with often excellent clarity.

28% est. supply
Myanmar Myanmar: Mogok Valley
Premium ★ Top Source

Royal blue, intense color and strong collector interest.

8% est. supply
Tanzania Tanzania: Merelani Hills
Notable

Diverse blue and fancy sapphire material; some bicolor stones.

8% est. supply
India Kashmir: Zanskar Range
Legendary ★ Top Source

Rarest and most prestigious blue sapphire origin; velvety cornflower blue, record auction prices, production largely ended around the 1930s.

1% est. supply
Cambodia Cambodia: Pailin
Commercial

Dark blue material similar to Thai/Cambodian basalt-related sapphire.

5% est. supply
Madagascar Madagascar: Ilakaka / Andranondambo region
Major

Major modern source with a broad quality range.

25% est. supply
Australia Australia: New South Wales / Queensland fields
Commercial

Often darker blue to blue-green; generally lower prestige than classic metamorphic sources.

15% est. supply
Thailand Thailand: Chanthaburi / Kanchanaburi
Commercial

Dark blue commercial material, often heat treated; also major trading/cutting hub.

8% est. supply
United States USA: Montana sapphire fields
Premium ★ Top Source

American origin producing naturally unheated sapphire; Yogo Gulch cornflower blue is iconic.

2% 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

Chelsea Filter Quick chromium test, key for emeralds and rubies 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 Spectroscope Reads characteristic absorption lines, confirms chromium, iron, copper UV Lamp, Long Wave and Short Wave Fluorescence exposes treatments, synthetics, and origin