What is a blemish on a gemstone?
By Jared James · Last updated 21 May 2026
Definition
A blemish is a flaw or irregularity on the external surface of a gemstone, as distinct from an inclusion, which is an internal characteristic. Blemishes include scratches, pits, nicks, chips and abrasions, and they affect how a stone looks under magnification and in certain lights. In diamond grading, blemishes are assessed alongside inclusions to determine the overall clarity grade. Minor surface blemishes can often be polished away without significantly affecting the stone, whereas deeper ones are more permanent.
Frequently asked questions
- What is the difference between a blemish and an inclusion?
- A blemish is on the surface of the stone, while an inclusion is inside the crystal. Both affect clarity, but inclusions are usually considered more significant because they cannot be polished away.
- Do blemishes affect a diamond's value?
- They do affect clarity grade, and by extension price, but minor surface blemishes matter less than significant internal inclusions. Many blemishes are only visible under 10x magnification and have little effect on how the stone looks to the naked eye.
- Can blemishes on gemstones be repaired?
- Light surface scratches and small abrasions can often be polished out by a lapidary without much loss of carat weight. Chips near the girdle are trickier and may require re-cutting, which changes the weight and potentially the proportions.
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