What is extinction in a gemstone?
By Jared James · Last updated 21 May 2026
Definition
In gemmology, extinction refers to the dark or black patches visible inside a coloured gemstone where light is absorbed and not returned to the eye. It happens because of how a stone's crystal structure interacts with light at certain angles, and in strongly pleochroic or doubly refractive stones it can be quite pronounced. A small amount of extinction is normal and expected, but heavy extinction across a large portion of the stone makes it look dull and lifeless, which reduces its appeal and value.
Frequently asked questions
- Is extinction in a gemstone a flaw?
- Not exactly a flaw in the clarity sense, but heavy extinction does reduce a stone's visual appeal. It is a natural optical property of many coloured gems, and a good cut can minimise it by orienting the stone to show the least extinction face-up.
- Which gemstones show the most extinction?
- Strongly pleochroic stones like alexandrite, tanzanite and some sapphires can show noticeable extinction. The effect is also common in rubies and other corundum, particularly in stones that have not been cut to minimise it.
- How can extinction be reduced in a gemstone?
- A skilled cutter will orient the rough so the finished stone faces up with as little extinction as possible. The shape and proportions of the cut play a big role in how much dark area the eye sees.
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