Zircon

Natural zircon occurs in honey brown, golden yellow, green, red, colourless and, most familiar commercially, vivid blue, the last produced by heating brownish material. Sri Lanka's gravels yield zircons in yellows, browns, greens and colourless stones. Zircon's optical properties give it exceptional life: high refractive index, strong dispersion producing rainbow fire, and birefringence so pronounced that back facet edges appear doubled under a loupe, a classic identification clue. The species also spans so-called high and low types, reflecting how much natural radioactive trace elements have altered the crystal structure over geological time; green stones are often the lower, metamict type with correspondingly lower property ranges.

Zircon quality rests on colour, clarity, cut and, unusually, condition of the material itself. Vivid blues and clean colourless stones are commercial favourites, while collectors also prize honey, golden and red stones. Eye-clean clarity is expected in most colours. Because of the gem's strong birefringence, cutting orientation matters, a poorly oriented stone can look fuzzy from facet doubling, while a well-cut zircon sparkles brilliantly. Zircon is noticeably dense, so stones face up smaller than their carat weight suggests compared with lighter species. Fine untreated colours and well-preserved crystals attract collector interest, and laboratory reports usefully confirm identity, treatment and that the stone is zircon rather than any imitation.

Heating is the defining treatment of commercial zircon: most blue and many colourless stones on the market are produced by heating brownish material, a long-established practice associated with South-East Asia. The resulting colours are generally stable, though some heated stones can revert slightly with prolonged strong light, a point worth asking about. Under international trade standards, notably CIBJO's Gemstone Book, one of the Blue Book standards published by the World Jewellery Confederation, treatments should be disclosed at every stage of sale, and consumer-protection law in many jurisdictions separately requires material facts such as treatment to be disclosed. Untreated natural colours, including Sri Lanka's honey, yellow and green stones, appeal to collectors precisely because they are unenhanced. Laboratory testing confirms treatment where detectable and, importantly, separates natural zircon from cubic zirconia and other simulants that borrow its reputation.

Sri Lanka has produced zircon for centuries from its gem gravels, and the colourless stones cut from material found near Matara in the island's south were historically sold as Matara diamonds, a name now recognised as a misnomer for what is a beautiful natural gem in its own right. Production continues from areas such as Ratnapura, Elahera and Okkampitiya. Cambodia and Thailand are the historic centres of the blue heated-zircon trade, with further supplies from Myanmar, Tanzania and Madagascar. Zircon is also of great scientific importance, as the mineral's crystals are among the oldest dated materials on Earth.

Zircon needs slightly more thoughtful care than its brilliance suggests. Hardness ranges from about 6 in metamict stones to 7.5 in high-type material, and the gem is brittle, with facet edges prone to chipping and abrading, a wear pattern the trade calls paper wear when stones rub together. Avoid ultrasonic and steam cleaning; wash gently in warm soapy water with a soft brush. Some heat-treated stones can shift colour under prolonged intense light or heat, so avoid leaving zircon jewellery in strong sunlight. Store each piece separately, choose protective settings for rings, and reserve zircon rings for occasional rather than rough daily wear.