clay — mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure …
cleiophane — old name for a light-coloured sphalerite; see cleiophane in ‘Classification’ …
clinochlore — species of mineral; data …
clinohumite — species of mineral; see clinohumite in ‘Classification’ …
clinozoisite — species of mineral; see clinozoisite in ‘Classification’ …
cobaltite — species of mineral; data; faceted specimens reported (Iverson, 2012) …
cobaltoan smithsonite — variety of smithsonite; see cobaltoan smithsonite in ‘Classification’ …
coffin — rare shape in faceting a gemstone …
colemanite — species of mineral; data; faceted specimens exist …
colour change garnet — variety of pyrope-spessartine series; see colour change garnet in ‘Classification’ …
cordierite — species of mineral; see cordierite in ‘Classification’ …
corundum — species of mineral; see corundum in ‘Classification’ …
cristobalite — species of mineral; data; constituent of opal …
crown — the upper part of faceted stone …
cubanite — species of mineral; data; faceted specimens exist …
culet — the bottom end of the pavilion of faceted stone …
culet facet — facet at the bottom end of the pavilion of faceted stone; very rare element in the contemporary design …
cuprite — species of mineral; data; faceted specimens reported …
cushion — a commonly used shape in faceting a gemstone …
cushion triangle — a commonly used shape in faceting a gemstone …
