cabochon

n. polished precious stone (without facets)

A cabochon or cabouchon is a gemstone which has been shaped and polished as opposed to facetted. The resulting form is usually a convex top with a flat bottom. Cutting "en cabochon" is usually applied to opaque gems, while facetting is usually applied to transparent stones. Hardness is also taken into account as softer gemstones with a hardness lower than 7 on the Mohs hardness scale are easily scratched, mainly by silicon dioxide in dust and grit. This would quickly make translucent gems unattractive. Instead they are polished as cabochons, making the scratches less evident.
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Noun
1. a highly polished convex-cut but unfaceted gem
(hypernym) gem, gemstone, stone

n. cabochon, polished precious stone

n. cabochon, polished precious stone