gemology
Gemology or gemmology is the science dealing with natural and artificial gemstone materials. It is a geoscience and a branch of mineralogy. Some jewelers (and many non-jewelers) are academically trained gemologists and are qualified to identify ...
, a culet is a flat face on the bottom of a gemstone.
During the 14th century, after the adoption of the table cut, a further
facet
Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cu ...
was added to the bottom of the cut parallel to the surface of the table. The term used for these bottom facets derives from the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...
word for bottom, ''culus''.
The culet is added largely to protect the integrity of the gemstone. On a diamond, the cleavage plane runs parallel to the
octahedral
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...
faces, and so any damage to the tip of the diamond could cause a split up the entire length of the pavilion. With other gemstones that are not subject to cleavage, the culet is added to protect the fragility of the pointed tip.
The culet has remained optional on many
diamond cut
A diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape (pear, oval), but the symmetry, proportioning and polish of a diamond. The cut of a diamond greatly affects ...
s up to the present day, and was omitted from Marcel Tolkowsky's original designs for the
round brilliant
A brilliant is a diamond or other gemstone cut in a particular form with numerous facets so as to have exceptional brilliance. The shape resembles that of a cone and provides maximized light return through the top of the diamond.
Even with mod ...
diamond cut in 1919. Nonetheless, culet facets are common on modern brilliant-cut diamonds.