Under 10x magnification, every diamond tells on itself. The internal characteristics — inclusions — and external characteristics — blemishes — are what clarity grading measures, and each has a name that gemmologists use the way doctors use anatomy. Learning these names is learning to read a stone.
Internal characteristics (inclusions)
- Feather — a separation or break due to either cleavage or fracture, often white and feathery in appearance; the classic inclusion buyers ask about.
- Included crystal — a mineral crystal contained within the diamond, coloured or colourless like its host; a gemstone inside a gemstone.
- Pinpoint — a very small inclusion seen at 10x as a tiny dot, singly or in groups or strings.
- Cloud — a hazy or milky area made up of a number of very small inclusions; what the eye reads as milkiness.
- Cavity — a large or deep opening; chip — a small or shallow opening, usually at the girdle edge.
- Bruise — surface crumbling, often accompanied by tiny root-like feathers.
- Bearding — tiny feathers extending inward from a bruted girdle (called hairline feathers on a polished or faceted girdle).
- Needle — a long, thin included crystal reaching the surface of a fashioned stone.
External characteristics (blemishes)
- Scratch — a linear indentation seen as a fine white line, curved or straight, in reflected light.
- Abrasion — tiny chips along facet junctions, turning sharp facet edges into white fuzzy lines.
- Natural — part of the original crystal surface left on the polished stone; evidence of the rough, not a defect of the cutting.
- Extra facet — a facet placed without regard for symmetry and not required by the cutting style.
- Polish lines — tiny parallel ridges or grooves confined to a single facet, from crystal-structure irregularities or the polishing itself.
- Pit — a tiny opening that looks like a white dot in reflected light; nick — a notch near the girdle or a facet edge.
Why the names matter
Each diamond's characteristics differ in type, size, shape, quantity, position and relief — no two are ever the same, making every stone a fingerprint. The type and position of a characteristic determines not just the grade but the durability story (a feather near the girdle is a different stone than a pinpoint deep in the pavilion) and the price conversation. This vocabulary is exactly what a gemmologist is trained to see — and what a buyer can learn to ask about before the certificate is even opened.
Grounded in the JDMIS Gemmology (GT104 Value Factors in Diamonds) seminar materials. Train your eye in Gem Identification Methods; for the grading framework around these characteristics, see The 4 Cs of Diamonds and How to Test Gemstones.