A cabochon (/ˈkæbəˌʃɒn/), from the Middle French word caboche (meaning "head"), is a gemstone which has been shaped and polished as opposed to faceted. The resulting form is usually a convex (rounded) obverse with a flat reverse.
This shape is used to bring out the incredible cat's eye (chatoyancy) or star effect (asterism) in certain gemstones.
Cabochon 22.41ct star sapphire from Sri Lanka.
Cabochon 3.94ct cat's eye chrysoberyl from Sri Lanka
Cabochon 22.15ct blue sapphire from Sri Lanka