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.
When jewellery is said to be shell, it usually refers to shimmering lining of any of a variety of shells. Abalone shell is beautifully coloured in blues, greens and purples, other shells have an iridescent white lining that shimmers with silky rainbow colours. Shell use in jewellery is usually as a slice of shell set in a bezel to protect its edges, or as a background underlay to other gems or metals. Sometimes the whole shell is carved and used in jewellery, not just the lining.
These earrings and a matching necklace are available right here from Alyssum Jewellery. Contact us to have the earrings converted to clip-on, if required.
Shell pearls are artificially created pearls formed from the inner lining of oyster shells (mother of pearl) that are ground to a powder before being reformed and polished into the shape of a pearl. Being manufactured in this way means they can be produced to any size or colour. They're inexpensive and a popular alternative to wild or farmed pearls.
Sillimanite, also called fibrolite or bucholzite, is a fibrous mineral that often occurs in needle-like crystals, found in Myanmar, Madagascar, United States, and many places in Europe. It is usually a glassy green, white or brownish colour, though specimens found in Sri Lanka can be a lovely pale sapphire blue.
As a gemstone, it's strong and durable but not widely known as Sillimanite is relatively rare.
Sinhalite is a relatively recent discovery, first noted in Sri Lanka in 1952. It's a translucent gemstone occurring in light pinks to yellowish-browns, and highly suited to faceting and jewellery use, though quite rare. Prior to 1952, Sinhilite had been thought to be a variant of peridot until laboratory testing proved it to be a gemstone in its own right.
Smithsonite is a zinc ore mineral, once thought to be the same as calamine. It rarely forms crystals and so isn't used in the jewellery trade, but is of more interest to collectors and mineralogists. Usually clear or white, in can occur in many colours depending on the inclusions present.
Smoky Quartz refers to quartz gemstones that occur in 'smoky' colours from greyish-brown to almost black. See our Gemology guide for the letter Q for more information.
Sodalite is a blue-white opaque mineral with a high sodium content. It's soft enough to be carved and polished so is often used as an ornamental stone rather than in jewellery. When sodalite is used for jewellery, it is polished en cabochon or carved into beads. As a jewellery gem, it is considered to be "poor man's lapis lazuli" owing to its similar appearance but much smaller price tag.
South Sea Pearl
A pearl specifically from the pinctada maxima oyster – a large oyster found in warm shallow seas around Western Australia, the Philippines, Indonesia and Southern India. The pearls from these molluscs are large with a lustrous nacre. Naturally found pearls can have an exceptionally high value because of the rarity of finding an oyster with a pearl in the wild, so most of the South Sea Pearls on sale are cultivated in pearl farms.
Spectrolite is a variety of labradorite (see our Gemology guide for the letter L) usually found in Finland.
Spessartine / Spessarite
A name given to a form of garnet. There are many forms or garnet, with the distinction really only being noted by scientists, gemologists, and those in the gemstone trade.
Sphalerite is a difficult mineral to identify as it often masquerades as other forms of black zinc sulphide. Sphalerite is an important ore of zinc, and despite most commonly occurring as a translucent black, it can also be found in an array of other colours, whose crystals are prized for their gemstone quality. As a gemstone it is not particularly durable, being only a 3.5-4 on the Mohs hardness scale, but in the hands of a skilled lapidary (gem cutter) it has a light dispersion and 'fire' three times greater than that of diamonds.
Sphene / Titanite
Sphene, also known as Titanite, is a gemstone with a fire brighter than a diamonds, but a relatively softer composition. It's suited to faceting and jewellery use if set carefully in a piece that is low impact, such as earrings. Sphene occurs most often in soft yellows, greens and oranges depending on where in the world it originates, though it is also found clear, grey, pink and black.
Spinel / Spinell
For a very long time spinels were often misidentified as ruby or sapphire, being found in the same deposits and in the same array of colours, but lab identification has proven them to be different minerals. Many of the precious sapphires and rubies in historic national treasures, such as the ruby in the centre of the British Imperial Crown, have since been proven to be spinel.
Spinel is slightly softer than sapphire and ruby (both second only in hardness to diamond), but still highly durable and perfect for jewellery use. Most spinel occurs in red (previously thought to be ruby); yellow, pink, purple or blue (like sapphire); or even colourless 'white' like diamond. Spinel has been found in areas all over the world.
White spinel is an alternative birthstone to April's diamond.
Spodumene is a lithium ore which forms highly prized crystals of gemstone quality. In its pink form, spodumene is called Kunzite (see our gemology guide to gemstones beginning with K), and in a green form it is hiddenite. These gemstone quality formations are not its most common state, and usually spodumene is pretty dull. Spodumene crystals can grow very large - the largest found was 12.8 meters high!
Many gemstone varieties have needle-like inclusions called 'rutile'. Sometimes these 'rutile' form long lines that intersect in a 6-pointed or 12-pointed star in a phenomenon known as asterism. Gemstones displaying asterism are known as 'star' gemstones, i.e. star ruby, star sapphire, star moonstone etc.
Stichtite is a pretty stone-like mineral, very soft and not suited to faceting, but frequently polished into cabochons for jewellery use. It occurs in deep pinks, lavender, and striking purples. Because it occurs in quite large formations, it is often carved into decorative display pieces.
Stichtite was first discovered in Tasmania in 1910 by the Mount Lyell Mining and Railway Company, and is often found in the same deposits as Serpentine.
Sugilite is a relatively rare pink-purple mineral first described in Japan in 1944. It can also be found in Canada and South Africa. Although most often occurring in amethyst colours due to the presence of manganese, it is also known to form in yellowish-browns and pinks. Most sugilite is opaque, in which case it is polished en cabochon, tumbled, or carved into beads, but occasionally sugilite is translucent and suited to faceting, though these gemstones would be very rare and expensive.
Sunstone is a variety of feldspar, occurring most often in shades of warm orange, though occasionally found in greens and blues too. Gemstone quality sunstone is usually transparent and emits tiny flashes of fire, like the sun's rays, giving the gemstone its name. These tiny flashes come from inclusions of copper and hematite which reflect the light back at the observer. Sunstone is also known as heliolite, after Helios – the God of the Sun in Greek mythology.
In jewellery use, sunstone is often polished en cabochon, or cut by a skilled lapidary to best display its aventurescence (light flashes), but being relatively soft, jewellery use is often limited to low impact pieces like earrings, brooches or pendants.