sunstone — a rock; see sunstone in ‘Classification’ …
sussexite — species of mineral; data; faceted specimens exist …
syenite — a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts (less than 5%) …
synthetic — not a natural gemstone; may be a product of hydrothermal synthesis …
taaffeite — synonym of magnesiotaaffeite-2N’2S …
table — wide flat facet in the middle of the crown of faceted stone …
tactite — a contact metamorphosed carbonate rock …
tantalite-(Mn) — species of mineral; data; faceted specimens exist …
tanzanite — variety of zoisite; see tanzanite in ‘Classification’ …
tapered pentagon — rare shape in faceting a gemstone …
tektite — natural glass; see tektite in ‘Classification’ …
tenebrescence — the ability of minerals to change colour when exposed to sunlight …
tetrahedrite — species of mineral; data; faceted specimens exist …
thaumasite — species of mineral; data; faceted specimens exist …
tiger’s eye — a rock; see tiger’s eye in ‘Classification’ …
titanite — species of mineral; see titanite in ‘Classification’ …
topaz — species of mineral; see topaz in ‘Classification’ …
translucent — clarity grade in gemstones; allow light to pass through, can be heavily included; some gems are naturally translucent …
trapeze — rare shape in faceting a gemstone …
tremolite — species of mineral; data; constituent of nephrite …
