cut corner triangle — a shape in faceting a gemstone …
cymophane — variety of chrysoberyl; see cymophane in ‘Classification’ …
danburite — species of mineral; see danburite in ‘Classification’ …
datolite — species of mineral; see datolite in ‘Classification’ …
decagon — rare shape in faceting a gemstone …
demantoid — variety of andradite; see demantoid in ‘Classification’ …
diabase — a mafic, subvolcanic rock; equivalent to volcanic basalt …
diagenesis — the change of sediment or existing sedimentary rocks into sedimentary rock during and after rock formation, at temperatures and pressures less than that required for the formation of metamorphic rocks …
diamond — species of mineral; see diamond in ‘Classification’ …
diaspore — species of mineral; see diaspore in ‘Classification’ …
dike — a sheet of rock that formed in a crack in a pre-existing rock body …
diopside — species of mineral; see diopside in ‘Classification’ …
dodecagon — rare shape in faceting a gemstone …
dolomite — species of mineral; see dolomite in ‘Classification’ …
dravite — species of mineral; see dravite in ‘Classification’ …
dumortierite — species of mineral; data; faceted specimens exist …
eclogite — a mafic (basaltic in composition) metamorphic rock …
elbaite — species of mineral; see elbaite in ‘Classification’ …
emerald — variety of beryl; see emerald in ‘Classification’ …
