rutile — species of mineral; see rutile in ‘Classification’ …
sandstone — a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains …
sanidine — species of mineral; see sanidine in ‘Classification’ …
sapphire — variety of corundum; see sapphire in ‘Classification’ …
sapphirine — species of mineral; see sapphirine in ‘Classification’ …
scapolite — generally refers to just the marialite-meionite series …
scheelite — species of mineral; see scheelite in ‘Classification’ …
schist — a metamorphic rock with medium to large grains of mica flakes …
schorl — species of mineral; see schorl in ‘Classification’ …
scolecite — species of mineral; see scolecite in ‘Classification’ …
sedimentary rock — one of the three main rock types; formed by the deposition of material at the Earth’s surface and within bodies of water …
sellaite — species of mineral; data; faceted specimens exist …
seminavette — rare shape in faceting a gemstone …
seraphinite — variety of clinochlore …
serendibite — species of mineral; see serendibite in ‘Classification’ …
serpentine jade — a rock; see serpentine jade in ‘Classification’ …
shale — a fine-grained sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite …
shield — rare shape in faceting a gemstone …
