50 Fun Facts About Gemstones

Which purple stone, its Greek name meaning 'not drunk', was a 'cardinal' gem until Brazilian finds made it common?

Amethyst sat with diamond and the big coloured stones as one of five cardinal gems until the 18th century, when Brazil's huge deposits made it cheap. Anglican bishops still wear amethyst rings, a nod to the Apostles being 'not drunk'.

Which blue-violet gem, found in 1967 in the Mererani Hills, did Tiffany & Co. rename and launch in 1968?

Tanzanite is the name Tiffany & Co. gave blue-violet zoisite in 1968, judging the mineral's real name too unappealing to sell. The whole supply comes from one deposit about 7 km long, and in 2002 it became December's newest birthstone.

Which aluminium-oxide mineral goes by one gem name when red and another in every other colour?

Corundum gives the world two of the four precious stones: its chromium-red crystals and the sapphires of every other colour, blue included. The name comes from the Tamil word kurundam, and at 9 on the Mohs scale only diamond is harder.

Which word comes from 'elektron', the Greek for amber, because the rubbed resin takes a static charge?

Electricity, electric and their relatives all descend from elektron, the Greek for amber, which bears a static charge when rubbed. Persian called the stone kah-ruba, 'straw-snatcher', and that word became the Arabic for electricity too.

Which gem, classed as a mineraloid because it has no crystal structure, did NASA announce in 2008 it had found on Mars?

Opal deposits on Mars were announced by NASA in late 2008, the same year a big new opal field turned up near Wegeltena in Ethiopia. Opal is hydrated silica with no crystal structure, so it counts as a mineraloid rather than a mineral.

The first working laser, built by Theodore Maiman in 1960, used a synthetic rod of which gem as its light source?

Ruby, grown synthetically, was the gain medium in the laser Maiman fired at Hughes Research Laboratories on 16 May 1960. A xenon flashtube pumps the rod with light, and the chromium atoms that colour the crystal red do the lasing.

Which royal bride chose her own 12-carat oval sapphire ring from Garrard, the ring William gave Catherine in 2010?

Diana Spencer picked the ring herself in 1981: a 12-carat oval blue sapphire ringed by 14 diamonds in 18-carat white gold, made by Crown jewellers Garrard and like her mother's. William proposed with it in 2010.

Which mineral did the ancient Greeks call 'krystallos', thinking its clear form was ice frozen too hard to melt?

Quartz was krystallos, from kryos, 'icy cold', because Theophrastus and others believed clear rock crystal was permanently frozen water, an idea Pliny the Elder still held. Every 'crystal' in English descends from that mistake.

A pearl is built up in layers of which iridescent material, the same stuff that lines a mollusc's shell?

Nacre, better known as mother of pearl, is laid down by the same living process whether it coats the shell's interior or wraps an intruder into a pearl. It is calcium carbonate, mostly aragonite, deposited in concentric layers.

Which country, home to the Muzo mines, produced 47% of the world's emeralds in the decade to 2005?

Colombia has long been the world's largest emerald producer, though its share has slipped for want of new finds and modern mining. Its mines also yield rare 'trapiche' emeralds, marked by ray-like spokes of dark impurities.

The 423-carat Logan Sapphire, the size of a chicken egg, came from which island, original home of the padparadscha?

Sri Lanka produced the Logan Sapphire, which Rebecca Guggenheim gave to the Smithsonian in 1960 set in a brooch ringed by 20 diamonds. The island's pink-orange padparadscha is the priciest of all the fancy-coloured sapphires.

Which pale-blue gem shares the beryl family with emerald, its largest known example being Brazil's Dom Pedro?

Aquamarine shares the beryl family with emerald and heliodor, and is common enough to be the affordable one. The largest known, the Dom Pedro, was found at Pedra Azul in Minas Gerais, Brazil, in the late 1980s.

Which green gem, an August birthstone, turns up inside pallasite meteorites as well as in volcanic basalt?

Peridot is gem-quality olivine, the magnesium-rich forsterite, and stones born in meteorites carry less lithium, nickel and zinc than volcanic ones. Gem-grade crystals are rare on Earth because olivine breaks down so readily at the surface.

Which January birthstone, really a family of minerals, is named for the pomegranate, whose red seeds it resembles?

Garnet has been cut for gems and crushed for abrasives since the Bronze Age, and its species span 6 to 7.5 on the Mohs scale. Certain garnets serve as indicator minerals in the hunt for diamonds.

Diamond is not forever: at room temperature and pressure it is metastable and slowly turns into which form of carbon?

Graphite is the stable form of carbon under everyday conditions, but diamond converts to it at a negligible rate, so the change is academic. In graphite the atoms bond in planes that slip past each other, which is why it is soft.

Which cut polishes a gem into a smooth dome instead of facets, the way to show a star or a cat's eye?

Cabochon, from the Middle French for 'head', was how every gem was finished before faceting was invented, and it is still the cut for opaque stones. The dome shows the star in a star sapphire that faceting would hide.

A diamond's rainbow flashes, which jewellers call 'fire', come from which optical property of the stone?

Dispersion, the splitting of white light into colours, is what the trade calls fire, and diamond has an unusually high value of it alongside its high refractive index. Early cuts like the rose barely showed it; the brilliant was built to.

Jet, the black stone Queen Victoria wore in mourning for Prince Albert, is a form of what?

Fossil wood, squeezed over millions of years into lignite, the lowest rank of coal, is what jet is, mostly from trees akin to the Chilean pine. It became fashionable in the 1850s and gave English the phrase 'jet-black'.

Red 'precious' coral, the Corallium rubrum carved into jewellery since antiquity, grows mainly in which sea?

Mediterranean waters are the main home of Corallium rubrum, which grows on dark rocky seabeds in the depths or in caves. Coral jewellery turns up in prehistoric European burials, and the material is too soft to facet, so it is cut as beads.

The Sar-i Sang mines, which have supplied lapis lazuli since the 7th millennium BC, lie in which modern country?

Afghanistan's Badakhshan province supplied the lapis in Tutankhamun's funeral mask and served the ancient Persian and Mesopotamian civilisations, and its mines still dominate the trade. Sar-i Sang sits in the Kokcha River valley.

Which pigment, ground from lapis lazuli, did Renaissance painters reserve for the Virgin Mary's clothing?

Ultramarine, made by grinding lapis imported from the end of the Middle Ages, was used by Masaccio, Titian and Vermeer, and has even turned up in the dental tartar of medieval nuns, probably from licking their brushes.

Pliny the Elder claims which queen dissolved a pearl worth millions of sesterces in vinegar to win a dinner-party bet?

Cleopatra pulled a stunt that works in chemistry as well as legend: pearls are mostly calcium carbonate, which reacts with the acetic acid in vinegar to give calcium acetate and carbon dioxide. Pliny tells the tale in his Natural History.

Moissanite, first found in 1893 in rock from Arizona's Meteor Crater, is a natural form of which compound?

Silicon carbide crystals from the crater were first taken for diamonds by Henri Moissan, who only identified them correctly in 1904. Edward Acheson had already made the compound artificially in 1891, two years before the natural find.

Which Washington socialite bought the Hope Diamond from Pierre Cartier in 1911, curse stories and all?

Evalyn Walsh McLean paid over $300,000 after Cartier's slow-burn presentation; the tales of a cursed origin were most likely invented in the early 1900s to add mystique and lift the price. Harry Winston bought it from her estate in 1949.

The 563-carat Star of India, stolen from New York's natural history museum in 1964, turned up months later where?

A Miami bus locker gave up the uninsured Star of India in January 1965, when one of the thieves, seeking leniency, led police to it. The 1964 raid also took the Midnight Star and the Eagle Diamond.

The Regent Diamond, mined in India and cut in London, was mounted on the sword guard of which French ruler in 1801?

Napoleon redeemed the Regent in 1801 and had goldsmiths Odiot, Boutet and Nitot set it in his sword guard; by 1812 it sat on his two-edged sword. His second wife, Marie Louise, carried it off to Austria when he was exiled.

The 'modern' birthstone list most jewellers still use was adopted in August 1912 at a jewellers' meeting held where?

Kansas City hosted the National Association of Jewelers, now Jewelers of America, when it fixed the list that one author called 'nothing but a piece of unfounded salesmanship'. Tiffany had printed birthstone poems as early as 1870.

Which of jade's two minerals did China carve for millennia before Burmese jadeite arrived in quantity around 1800?

Nephrite, the white 'Hetian jade' Khotan sent as yearly tribute to the imperial court, kept its hold on Chinese scholars even as Qing aristocrats fell for the greens of jadeite. The name comes via Latin from the Spanish piedra de ijada.

Alexandrite, green by daylight and red under incandescent light, is a rare variety of which mineral?

Chrysoberyl, a beryllium aluminate at 8.5 on the Mohs scale, is a different mineral from beryl despite the name; its other famous variety is cat's eye. Alexandrites over five carats were once thought to come only from Russia's Urals.

Which Myanmar valley, forced open by the British in 1886, was for centuries the main source of 'pigeon's blood' stones?

Mogok lost its crown in the 1990s, when Mong Hsu in central Myanmar began producing and quickly became the world's main mining area for the stone. 'Pigeon blood', the brightest red, still commands a big premium over other grades.

Neon-blue 'Paraíba' tourmaline, named after a Brazilian state, owes its electric colour mainly to which metal?

Copper drives the colour, and a blue tourmaline that is diamagnetic can be told apart from the magnetic, iron-coloured blues. Much so-called Paraíba stone actually comes from the neighbouring state of Rio Grande do Norte.

The pink-orange sapphire called padparadscha, the priciest of the fancy colours, is named after which flower?

Lotus blossom, Nelumbo nucifera, is what the Sanskrit name padma ranga describes, and the rarest padparadschas are the wholly natural ones with no sign of treatment. Since 2001 beryllium diffusion has put more of the colour on the market.

The six-rayed star in a star sapphire is usually caused by fine needle inclusions of which titanium-dioxide mineral?

Rutile needles reflect light into the star, and the rare twelve-rayed stars come from a second set of inclusions, platelets of hematite, which add a golden star to the whitish one. The effect is called asterism.

Which country's Mount Smaragdus mines, worked on an industrial scale by Rome, supplied the ancient world's emeralds?

Egypt's mines on Mount Smaragdus were worked from 1500 BC, then industrially by the Roman and Byzantine empires and later by Islamic rulers. They were abandoned once far richer deposits turned up in South America; only ruins remain.

The Amber Room, which vanished in World War II, was a 1716 gift to Peter the Great from which kingdom's ruler?

Prussia's Frederick William I gave Peter the room to seal a Russo-Prussian alliance against Sweden; it had been begun in 1701 for Berlin's Charlottenburg Palace. Modern valuations run from $142 million to over $500 million.

Which udon-seller's son produced his first cultured pearls in 1893, after years of failure at his Ago Bay oyster farm?

Kokichi Mikimoto created hemispherical cultured pearls on 11 July 1893, having started the farm with a loan in 1888 and his wife Ume as partner, and went on to found the luxury pearl company that still bears his name.

Deep-blue stones of which November birthstone mostly began pale or colourless, then were irradiated and heated?

Topaz in its orange form, 'precious topaz', is November's birthstone, a symbol of friendship and the state gem of Utah, while the blues on most jewellery counters owe their depth to the treatment lab.

Yogo sapphires, cornflower blue straight out of the ground and never heat-treated, are mined in which US state?

Montana's Yogo Gulch, west of Lewistown, yields stones that need no heating because their colour is right as found, and they are free of inclusions. Most North American sapphires come from the state's Missouri River and Rock Creek deposits.

Sapphires from which region's Paddar Valley, mined mainly around 1900, earn the highest premium of any origin?

Kashmir stones have a silky look and a blue that stays lustrous under any light, where other origins can turn purplish or grey. Sotheby's set a per-carat auction record for them of $240,205 in June 2015.

Which blue diamond, once in the Bavarian crown jewels, did Laurence Graff controversially recut in 2010 to remove flaws?

The Wittelsbach lost over four carats when three cutters reworked it and became the Wittelsbach-Graff; critics said its history was compromised, Graff that 'to create beauty is not a sin'. He had paid a record £16.4 million in 2008.

Which French chemist's flame-fusion process, made public in 1902, first grew synthetic gems on a commercial scale?

Auguste Verneuil had been Edmond Frémy's assistant from 1876 before developing the method alone in the 1880s, sealing his notes and publishing details only in 1904. Swiss 'Geneva' stones are now thought to be earlier flame-fusion products.

St Edward's Sapphire, reputedly from the Confessor's coronation ring, tops the cross on which piece of British regalia?

The Imperial State Crown has carried the stone in the cross above its monde since Victoria's 1838 crown, and it stays there in the 1937 version worn by Charles III. The gem was reputedly taken from the ring at Edward's 1163 reburial.

Tourmaline earned the nickname 'Ceylonese Magnet' by attracting and then repelling hot ash, thanks to which property?

Pyroelectricity, a charge that appears as the crystal warms or cools, is what pulled the ashes in; tourmaline's hemimorphic crystals are piezoelectric too, producing charge under pressure.

Which lilac variety of spodumene, found in 1902, honours Tiffany & Co.'s chief jeweller and noted mineralogist?

Kunzite gets its purple from traces of manganese, while its green sibling hiddenite is coloured by chromium; both show strong pleochroism, changing shade with the viewing angle. The mineral they belong to is a major ore of lithium.

Moonstone's floating sheen, 'adularescence', is named after a mining site near Mount Adular in which country?

Switzerland's Mount Adular, now the St Gotthard area, named adularia, the orthoclase feldspar behind most moonstone; the glow comes from light scattering between layers of two different feldspars. An older name is hecatolite, after Hecate.

Which natural gem, named from the Persian for 'gold-hued', bends light so strongly that its back facets look doubled?

Zircon's doubling is what lets a jeweller tell it from diamond and from the man-made cubic zirconia, which is harder at 8 to 8.5 against zircon's 7.5. Its natural colours run from colourless through golden, red and brown to blue and green.

Which diamond colour is the rarest and most expensive of all, with the 5.11-carat Moussaieff the largest known?

Red diamonds are rarer even than pinks and blues, so few have been found that most weigh under a carat, and decades of research have not settled what causes the colour. The Moussaieff Red came out of Brazil.

Gem dealers use which French word for the mossy-looking tangle of inclusions and fissures inside a typical emerald?

Jardin means garden, and because stones free of surface-reaching fissures are so rare, almost all emeralds are 'oiled' to fill the cracks and improve their apparent clarity.

Which oil, its refractive index close to the stone's, is the traditional filler for surface cracks in most emeralds?

Cedar oil is pressed into surface-reaching fissures after cutting to improve clarity and stability, a treatment so routine that untreated emeralds are extremely rare. Some graders ignore oil traces that do not improve the look of the stone.

Cutters can split a rough diamond with a single tap of a steel blade in a groove, exploiting which property?

Cleavage planes, mapped out at the planning stage, decide where the rough can be split cleanly, and the separated pieces then go on to bruting and polishing as separate gems. Cleaving is the first physical step in the cutting process.