A trilliant cut, sometimes called a trillion or trillian, is a triangular type of gemstone cut. The cut has many variations. It may have curved or uncurved sides. The shape of the top surface, or table, also varies.
The trilliant cut was introduced by the Asscher brothers in Amsterdam and was later trademarked by the Henry Meyer Diamond Company of New York in 1962. Now that the patent has expired, the term "Trilliant Cut" is used to refer to all triangular shaped gems, even step cut and cabochon stones. Triangular Brilliant and Triangular Modified Brilliant are the common terms used by GIA when referring to non-branded diamonds.
The cut displays a very sharp brilliance or fire if the diamond is cut to the correct depth allowing good scintillation. It is generally cut with a 1:1 length to width ratio with uncurved edges. This uncurved trilliant cut is usually used for accent gemstones, on either side of a main, larger stone of a ring.
This is a softer version of the uncurved version, with three soft points and curved sides. The length to width ratio should still be 1:1, keeping the gemstone proportioned. This cut is unusual, but can be found in pieces as a solitary gem or as an accent gem.