Gemstone Glossary

Table facet

Largest facet on the crown of a gemstone


Drop- or pearshaped stone with smooth surface; round or oval cross section

Total reflection

Aray of light, travelling from an optically dense medium (gemstone) into a rare medium (air) cannot leave the dense medium, if it hits the boundary between the two media at an angle greater than the critical angle.
In correctly cut gems this phenomenon causes light, which enters the gem through the crown to leave the stone through the crown, as well. too deep or too shallow pavilions cause severe loss of brilliance. Furthermore, a shallow pavilion produces an uncomely area of low reflection, the so-called "fish eye" or "window".
total reflection


transmitting some light

Trapiche emerald

A special form of emerald; the spanish word "trapiche" denotes the cogwheel with which sugarcane is crushed. In trapiche emerald inclusions of coal-black shale form a pattern resembling the spokes of a wheel. There are at least four types of trapiche emerald:

The phenomenon was also observed in rubies from myanmar (burma), India and vietnam

Trapiche emeralds from Colombia

trapiche rubin rubytrapiche rubin rubytrapiche rubin rubytrapiche rubin ruby

Trapiche rubies from South india


Tri-colouredness; a form of pleochroism

Trilliant cut

Also trillion, a triangular cut with outwardly curved sides. Has more or less replaced the classic straight-sided triangel as trilliants are much less susceptible to damage during cutting and setting.


Composite stone consisting of three parts. Most common in opal when a paper-thin layer of opal is glued onto a base of onyx or plastic and covered with a glass- or sometimes rock crystal top


Cheap gemstones are not polished by hand individually. Instead, they are tumble-polished in large quantities in rotating or vibrating tumbling machines which results in irregularly shaped "pebbles".