A knowledge of gemstones can only enhance your appreciation of jewellery and the other fine
and precious creations which use them.
Virtually all gemstones are formed beneath the earth from naturally occurring minerals.
Those that have outcropped on the surface, or been washed down in streams and rivers, have been used for personal adornment since time immemorial, and hundreds are now actively mined or synthesized.
The colour, sparkle and rare beauty of gemstones have fascinated mankind for thousands of years and are an integral part of some of our most collectable creations.
Gemstones range from precious diamonds, rubies and emeralds to the corals, turquoises and opals which were popular with the Victorians.
Jewellers have used a tremendous range of materials over the centuries to create their wares, depending on what they could find and the whims of fashion, but the flash and fire of gemstones, and the richness and iridescent subtleties of their colour, have ensured their popularity down through the ages.
In modern times, they have often been imitated in coloured glass or plastics, or synthesized in chemistry labs. Learning to recognize the real thing can save you from making some very expensive mistakes; when you go out buying, always take a magnifying glass with you and examine any gemstones carefully. If you've any doubts at all, leave the piece alone.
AMETHYST A member of the quartz family, amethysts can vary from pale lavender to deep violet in colour. The deeper the shade, the more valuable the stone; the finest are a rich purple, flashing with hints of red.
Used from antiquity for bishops' rings and for crucifixes, amethysts were also popular with the Georgians and early Victorians. They fell out of favour until the early 20th century, when they were a favourite stone of art nouveau designers, who combined them with opals and moonstones
for a delicate, moonlit effect. Glass imitations lack warmth and are generally a vivid mauve in colour.
CORAL Coral is not strictly a stone at all, but the external skeleton of the coral polyp, collected in the Mediterranean and off the coast of Japan. The colour ranges from white through pale pink (known as Angel Skin) to dark red. Capable of being carved and polished, coral is ideal for brooches (especially cameos), beads, rings and charms. In its natural, 'twiggy' state, known as branch coral, it was also used to make necklaces.
Coral was thought to be protection against witches and enchantment; good luck charms were often attached in bunches to a carved coral hand. Necklaces and suites of jewellery were made in ropes'; minute beads of coral were strung together, then these strands were twisted together. This type of jewellery was very delicate and difficult to repair, making it rare and costly
today. Imitation coral is general made of plastic, and is often far too orange. The real thing has a harder, more glassy feel.
DIAMOND The best-known of all gems, diamonds are an extremely hard crystalline form of carbon which
is created under enormous heat and pressure deep within the earth's crust. India was originally the main source of diamonds, followed by Brazil from about 1750. In 1867, they were discovered in South Africa, which now dominates the market.
Diamonds are measured by weight in carats - stones can be as small as
1/32 of a carat - and graded by colour. The most valuable ones are blue-white, and are known as diamonds of the first water. Next come the colourless variety, which have a hard whiteness. Stones with a yellow to brown tinge are less valuable.
Occasionally 'sports' turn up. These are diamonds in unusual colours such as canary yellow, bronze, blue, green, pink and even red. Green diamonds can also be created artificially by treating normal stones with radium.
The glittering, flashing quality of a diamond is partly due to the stone's nature and partly to the cutting employed.
Any cutting or cleaving must go with the grain of the stone if it's to retain its sparkle. Irregular or flawed stones can be sawed against the grain or in any desired direction. Before the 16th century, diamonds were often left in their natural state, which allowed little refraction and showed the stone as rather dull.
EMERALD A member of the beryl family, the emerald gets its green colour from traces of chromium. The best stones are a deep, rich green, though the colour ranges from a dark bottle green to grass green; anything paler is known as green beryl or aquamarine, though Russian emeralds have a yellowish tint.
Perfect specimens are rare and very valuable. Emeralds were found in India, Egypt and Central America, but later they were mined in Colombia and in Russia, South Africa, Brazil and Australia.
Take care when you're buying. A Brazilian emerald isn't an emerald at all, but a green tourmaline. Green garnets can also be mistaken for emeralds, while even experts can have trouble distinguishing synthetic emeralds from the real thing.
Emeralds should be treated with care as the surface is easily scratched or chipped, making the stone look dull. The stones benefit from step cutting, which is sometimes known as emerald cut; they lack the necessary fire for a brilliant cut.
GARNET Deep red in colour, garnets were a particularly popular gemstone with the Victorians. The stones were usually cut as cabochons (rounded on the top and flat on the back, with no facets) and the back was then hollowed out to give a brighter colour. The resulting stone was known as a carbuncle.
Suites of jewellery were made using the pyrope garnet, a dark red variety mined in Bohemia, in mainly floral designs. These garnets were also occasionally called Cape rubies.
Among the other members of the garnet family are the almandine garnet, which is more violet in colour, and the demantoid garnet, which has a green hue like a
OPALS The opal is an unusual stone; it's semi-transparent, not particularly hard and not crystalline in structure. It may shrink in time with loss of water. It is valued for its flashes of iridescent colour. The most valuable form is the opaque black opal, which is actually dark blue or green. The fiery colors show up vividly against the dark background. White or milk opals ar cloudy white and filled with tiny bubbles of gas, and their iridescence is more muted. Mexican water opals are almost colourless, while fire opals are orange-red in hue.
The 'pattern' seen in the opal is important. Harlequin has the same colour i l small regular patches which flash impressively. Pin-point has small patches and is not as vivid. Flame opal has
bands and streaks.
Although fire opals are sometimes facet-cut, others are always cut in a flattish cabochon. If the piece is thin, it may be hacked with a thicker piece, making a kind of sandwich known as a doublet. A triplet has a protective covering of clear crystal.
Opals are very porous and should be washed only in clean fresh water to retain their sparkle. They will absorb soapy water, spoiling the look of the gem. Comparatively soft, opals should be stored away from other jewellery.
MOONSTONES The most sought after moonstones are bluish with a milky tinge. Lesser quality stones are a rather dull grey, sometimes with a hint of yellow. The moonlit,
blue-silver sheen was enhanced by cutting the stones as cabochons and setting them in silver mounts.
Moonstones were particularly popular in the art nouveau
period, when the fashion was for light, delicate jewellery. They are often seen in conjunction with other stones, including
amethysts, aquamarines, chalcedony,
opals and freshwater or river pearls, and were frequently used to decorate the headings of
hair combs, or in earrings, rings and, most beautifully of all, in delicate pendants.
PERIDOTS Members of the olivine family, peridots are a bright, clear, almost lime green. They were most popular in the Victorian era when they were set in gold, mounted alone or with seed pearls, and used for delicate pendants or small brooches. They were usually cut in emerald style
for brooches and pendeloque (pearshaped) for pendants. A variety found in Arizona is golden brown.
RUBY Perfect rubies are clear and transparent. They are second only to diamonds in hardness and value, and large ones are more valuable than diamonds of the same size, as very few sizeable rubies are found to be free of flaws. The finest stones come from Burma and are a rich, dark, red, known as 'pigeon's blood'. Another dark ruby came from Siam (Thailand) and has a brownish tinge like the garnet. Some types of garnet are known as 'Ceylon', 'Bohemian', 'Colorado' or 'Arizona' rubies, and it's important not to be misled by this.
A pale, rose-coloured ruby is found in Ceylon, but what it lacks in depth of colour it makes up for in sparkle.
SAPPHIRE Like the ruby, the sapphire is a member of the corundum family. In ancient times it was known as
'hyacinthus', and in the Middle Ages it was thought to confer purity and goodness on those who wore it.
The most precious sapphires are a deep velvety or cornflower blue, and the Kashmir sapphire is the most desirable of these, though stones from Burma and Siam (Thailand) are also prized. Sapphires from NSW, in Australia, are very dark, almost black, and sometimes have an almost greenish tinge. Much paler stones come from Sri Lanka.
Not all sapphires are blue; various different colours occur when different metallic elements are present. Yellow sapphires resemble topaz, while white ones are sometimes used instead of diamonds. Mauve sapphires have a rather attractive amethyst colour, while green and pale pink varieties can also sometimes be found.
Star sapphires are used in rings. They are always cut as cabochons, with three lines crossing to make a six-pointed star. They are generally a cool pale blue, almost grey.
TURQUOISE Turquoise has been used decoratively for at least 5,000 years. In Victorian times it was known as the Turkey stone, from the country where it was mined. It can vary from a rich blue-green (a deep blue variety is known as Persian turquoise) to a pale
It's usually cut as a cabochon and set in gold, often combined with pearls. It was found in large quantities in Tibet, India and China, and was prized by the Aztecs. In Colorado and New Mexico it was set, uncut, in silver and worn by the native American peoples. Turquoise is porous and stones can easily be discoloured by grease or perfume.