What is a cabochon?

A cabochon refers to a gemstone that is shaped and polished but not faceted, characterized by a smooth, rounded, or domed top and a flat base. This method of cutting showcases the stone's color and texture, allowing for a vibrant and luminous appearance. Cabochons can be made from various types of gemstones, including opaque stones like opals and some jaspers, as well as translucent and transparent stones.

The other choices provide descriptions that do not accurately define a cabochon. Size standardization pertains to how gemstones can be measured or categorized by size, which is unrelated to the specific shaping and polishing technique of cabochon cutting. Crystal growth habit refers to the natural way in which crystals form within the earth, but it does not relate to the finished look of a gemstone. Lastly, while thin layers of precious opal have their own unique characteristics, they do not define what a cabochon is, which is more about the shape and cut of a gemstone than its material composition.