What is a flaw in a gemstone?
By Jared James · Last updated 21 May 2026
Definition
In gemmology, a flaw is a general term for any imperfection in a gemstone, whether inside or on its surface. Internal flaws are called inclusions and include crystals, feathers, clouds and needles trapped within the stone as it grew. External flaws are called blemishes and include scratches, chips, naturals and polish marks. All flaws are assessed by a gemologist under 10x magnification to assign a clarity grade, and their type, size, position and number determine how much they affect beauty and value.
Frequently asked questions
- Do all gemstones have flaws?
- Almost all natural gemstones have some inclusions or blemishes, though in higher clarity grades they may only be visible under magnification. Truly flawless gems are exceptionally rare in nature, which is part of why they command a premium.
- How do flaws affect a gemstone's value?
- Fewer and less visible flaws generally mean a higher clarity grade and a higher price, especially for diamonds. For coloured gemstones the rules are a little different, since some inclusions are acceptable and even expected in certain species like emerald, where eye-clean natural stones are genuinely rare.
- What is the difference between an inclusion and a blemish?
- An inclusion is inside the stone, while a blemish is on its surface. Both are considered flaws in the broad sense, but inclusions are generally given more weight in grading because they are harder to polish away and can affect the structural integrity of the stone.
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