Corundum
Ruby
Red, pinkish red, purplish red
Pink
Purple
Red
Optical characteristics
- Ref. index
- 1.762 – 1.77
- Birefringence
- 0.008 – 0.01
- Luster
- Vitreous
- Pleochroism
- Strong Strong dichroism: red to orange-red or purplish red.
- Fluorescence
- Often red under long-wave UV; iron-rich stones may be weak or inert.
Source localities
Myanmar
Myanmar: Mogok Valley
Legendary
★ Top Source
Classic source for ruby, sapphire, spinel and other collector gems.
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.
Tanzania
Tanzania: Merelani Hills
Major
Major source for tanzanite, garnet, spinel, tourmaline, ruby and fancy sapphires.
Vietnam
Vietnam: Luc Yen / Quy Chau
Premium
★ Top Source
Known for ruby, sapphire, spinel and rare gems.
Tanzania
Tanzania: Mahenge
Notable
Small alluvial ruby production alongside the spinel deposits.
Mozambique
Mozambique: Montepuez / Alto Ligonha / Cuamba
Major
Major modern source for ruby, garnet, tourmaline and Paraíba-type tourmaline.
Myanmar
Myanmar: Mong Hsu
Commercial
Major commercial ruby source producing heat-treated material; known for characteristic blue cores requiring high-temperature treatment.
Thailand
Thailand: Chanthaburi / Kanchanaburi
Commercial
Historic ruby and sapphire area and major cutting/trading center; many stones are heat treated.
Madagascar
Madagascar: Ilakaka / Andranondambo region
Major
Modern major source for sapphire, garnet, beryl, quartz, tourmaline and many collector gems.
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…
Composite Filling Lead Glass Filling
Lead glass filling turns very fractured ruby into a composite material. It is far…
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 & 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…
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