Gemology: S is for ...
Our 19th journey into the realm of gemology brings you the many gemstones beginning with S. Here we take a look at Saltwater Pearl , Sapphire, Sard, Sardonyx, Saussurite, Scapolite, Scheelite, Schorl, Selenite, Septarian, Seraphinite, Serpentine, Shell, Shell Pearl, Sillimanite, Sinhalite, Smithsonite, Smoky Quartz, Sodalite, South Sea Pearl, Spectrolite, Spessartine / Spessarite, Sphalerite, Sphene / Titanite, Spinel / Spinell, Spodumene, 'Star' Gemstones, Stichtite, Sugilite, Sunstone, and Swarovski.
Pearls are formed in molluscs that live in either freshwater (rivers) or saltwater (oceans and inlets). Saltwater pearls are from molluscs found in the sea.
Sapphire is the gemstone quality variant of the mineral corundum, occurring in many colours except red – red sapphires do exist, but they're called rubies! Sapphires are more widely known for being blue, so other colours have their name stated, i.e. green sapphire, pink sapphire, yellow sapphire etc.
Sapphires are very hard gemstones, second only to diamonds, and so are suited to a full range of jewellery uses. Sapphires can be translucent to opaque depending on the inclusions, with some sapphires displaying asterism (a star form within the gem, usually seen in opaque gems which are then polished en cabochon to enhance the feature), and pleochroism, the colour changing ability to appear one colour in natural light, and another colour in incandescent light, like Alexandrite.
Sapphire is the birthstone for September.
Sard is an orange-brown variant of chalcedony. It was named for the city of Sardis in Lydia, where it is commonly found, or from the Persian 'sered' meaning yellow-red. Sard generally occurs in one colour throughout. When it is banded with white it is known as sardonyx. Sard is fairly durable, but soft enough to be carved. In jewellery use it is usually polished en cabochon, or carved into beads.
Sardonyx is an orange-white striped variety of chalcedony. Its use has been popular through history where it has been carved through the layers into cameos and intaglios, with a background of orange and the relief in white, or vice-verse.
Saussurite is not a true mineral in its own right, but a combination of several other minerals which together form a greyish-green mineral often used a jade substitute. It was named for the Swiss explorer Horace Benedict de Saussure, who discovered what he thought was jade on the slopes of Mont Blanc in 1806.
Scapolite is the name given to two minerals that are very similar to each other and difficult to distinguish; meionite and marialite. It's a crystalline mineral occurring in pretty shades of yellow to lavender, but it's unstable and subject to disintegration when exposed to certain weather conditions, so entirely unsuited to jewellery use.
Scheelite is an orange-brown crystal that fluoresces under ultraviolet light. It occurs with tungsten, often containing tungsten within its composition. Flawless crystals are occasionally fashioned into gemstones, but they're not particularly hard so are mainly sought by collectors.
Schorl is black tourmaline in its darkest and most opaque form. It's the most common form of tourmaline and looks stunning when cut and polished into a gemstone.
Selenite is a crystalline form of the common mineral, gypsum. Nearly transparent to milky white in colour, its name comes from the Greek meaning moon stone. Although polished crystals can look beautiful and ethereal, it is very soft and not suited to jewellery use.
Septarian, also known as Dragon Stone or Dragon Egg, is a mineral formed millions of years ago in volcanic eruptions. It's an amalgamation of mud, minerals, and ancient sea life 'concreted' together into balls which look beautiful as a collectors piece when polished. The stones are often sliced or polished en cabochon for use in jewellery.
Seraphinite is the trade name for a particular variant of chlorite, with a feather-like chatoyancy resembling angel wings. It occurs in beautiful shades of moss green and is found only in the Siberian region of Russia. Seraphinite is often sliced, tumbled and polished for jewellery use, or polished into balls for decorative displays.
Serpentine is a form of magnesium silicate, usually green but also occurring in greyish-greens and brownish-greens. For jewellery use it is generally polished en cabochon or carved because its milky opaqueness is not benefited by faceting. Serpentine is found in many places worldwide, and has been popular throughout history.