SAPPHIRE
Sapphire
Corundum
Corundum in a wide range of colors, not only blue. Red corundum is classified separately as ruby.
GEM PROFILE
Basic properties
- Mineral or material
- Corundum
- Main chemical composition
- Al₂O₃
- Crystal & structure
- Trigonal
Crystals can form hexagonal plates or prisms. Some stones show pleochroism: different colors or intensities in different directions.
- Typical colors
- Blue, pink, yellow, orange, green, purple, colorless and more
- Mohs hardness
- 9
A measure of scratch resistance, distinct from resistance to impact or breakage.
About hardness and durability - Representative sources
Examples of known sources. Determining the origin of an individual stone requires examination and comparison with reference material.
- Common cutting styles
- Oval and cushion mixed cuts are common. Star sapphires are polished as cabochons.
Explore cutting styles
LOOK A LITTLE CLOSER
What to observe
Color zoning, pleochroism and fine needle-like inclusions called silk can be useful observations. Some sapphires display a star effect.
TREATMENT & CARE
Treatments & care
Treatments & identification
Heating, diffusion treatment and filling may be encountered. A color name alone does not indicate whether treatment has occurred.
Everyday care
Use a damp cloth for filled or dyed material. Confirm the treatment and condition before selecting a cleaning method.
Cleaning depends on treatment, inclusions and mounting. If a stone's condition is unknown, ask your jeweler or a gem specialist before cleaning.
READING & REFERENCES
References
Public sources for learning about this gemstone's general properties.
- GIA · Gemological reference
- GIA · Care & Cleaning
- Handbook of Mineralogy · Mineral data (PDF)
- GIA · Gem sources and fundamentals
This dictionary provides general educational information. Values are representative and do not identify or grade an individual stone. Locality examples include historical deposits.
Sources checked: October 19, 2026