culet
Culet is a term used in gemology and crystallography to refer to a small facet or basal face on a crystal or cut gem. In gemstones, a culet is the tiny facet at the bottom of a cut diamond or other faceted stone, opposite the table. The culet is typically very small and may be absent in a well-cut stone. When present, it can be described by size categories such as none, very small, small, medium, or large. A small culet is usually invisible to the naked eye; a large culet can appear as a dark dot from the crown and may affect light performance by allowing light leakage, reducing brightness. The choice to keep the culet small or zero depends on balancing durability, optical desirability, and cutting style. Historically, culets were considered protective to prevent the pavilion point from chipping during handling, but modern cutters often minimize or omit the culet.
In crystallography and mineralogy, culet also refers to the smallest basal or lowermost face of a crystal,
The term derives from the French culet, meaning a small tail or neck. In practice, culet considerations