Gem of the Month: Turquoise

tur_cab.jpgThe modern birthstone for December is Turquoise (traditional or alternative birthstones include blue topaz, zircon and tanzanite).  The example at left shows a beautiful sky blue colour with a dramatic black diagonal slash – from Aztec Moon.

Gemmology Matters:  Turquoise is a hydrated copper-aluminium phosphate with the chemical formula CuAl6(PO4)4(OH)8·5H2O.   Turquoise is a cryptocrystalline opaque mineral which is rare in gem quality.  Colour ranges from white through various blue colours to a yellowish green with the most valuable types usually considered to be a pure sky or “robin’s egg” blue with little green tone and even colour.   Colour type depends on the relative amounts of copper and iron in the stone with copper producing blue colour and iron producing green.  Although uniformity of colour is prized in turquoise, it is often found with brown/black veining or marks running through the stone – known as “Turquoise Matrix”, these types are usually worth less but may be considered more attractive by some buyers.

turqbluegem.jpgTurquoise is mined in the Southwestern United States, Iran, Tibet, and China.  Turquoise is usually found in dry regions and in association with copper deposits.  Particuarly in the USA, it is often mined as a by-product of copper mining.   Photograph at left shows a piece of turquoise from Nevada (image from Skystone Trading).   Australia is not a major source of turquoise with only small deposits found in northern Victoria, in the Narooma-Bodalla region of the New South Wales south coast, and at Amaroo station in the Northern Territory (Australian Museum).

Turquoise in its natural state is relatively soft at 5 to 6 on the Moh Scale.  It can be susceptible to damage or discolouration if exposed to prolonged sunlight, skin oils or chemicals in perfumes, cleaning agents, etc.  In order to protect against this, many turquoise gems are sealed with oil or wax.  A more radical form of this treatment is the creation of “bonded” or “stabilised” turquoise by impregnating the stone with epoxy or plastics under pressure.  Some turquoise is sold as “reconstituted” where small fragments of stone are ground and then bonded together to form a new stone – be aware that these types may include “filler” material and/or be dyed.  Imitations are also frequently used – the most common being white howlite dyed to imitate the blue of turquoise.  The cheaper turquoise used in beads or low-cost silver jewellery is usually heavily treated or may actually be imitation.  Very fine quality turquoise is rare and will command a high price – these stones should be verified by an expert.

Mythology and Lore:  Turquoise is among the worlds oldest known gemstones – many ancient civilisations valued it highly.  The name Turquoise is derived from the French “Pierre Turquois” meaning Turkish Stone as it was thought the gem came from Turkey.  Actually, the gems reaching Europe at the time came via marketplaces in Turkey from Persia (now Iran), where some of the oldest known turquoise mines are located.  In Persian, Turquoise is known as “Ferozah”, meaning victorious and it is the national gemstone of Iran to this day.

Ancient examples of its use survive to this day and it may seen in some of the most famous archeological artifacts.  The gold burial mask of Tutankhamun is heavily inlaid with gemstones of which turquoise features prominantly. The Aztecs also used the stone heavily and a number of examples of this work may be seen in work dating back to the time of Montezuma.

serpent.jpgtut.jpgImage at left is of Tutankhamun’s Burial Mask – courtesy of the Egyptian Museum.  Image at right is of an Aztec double-headed serpent with turquoise mosaic – see the British Museum image collection of artifacts from Montezuma’s Treasure.

Many Native American peoples used the stone as a protective amulet – it is often associated with the sky and wind.  It is said that Apache warriors believed wearing  turquoise would improve their hunting prowess.  Turquoise was generally believed to bring happiness and good fortune to all and in fact, it did bring great fortune to the Anasazi people who mined the stone due to the high demand for it from other areas such as Mexico.

The typical Native American turquoise set silver jewellery is a relatively modern development (thought to date from the late 1880’s) – traditional pieces were more likely to use turquoise as beads, inlay or mosaic on natural materials such as wood and carvings.

tur_brac.jpg

However these days, the use of silver to complement the unique beauty of turquoise is closely associated with southwestern American culture and the popularity of this style of jewellery has spread worldwide.  This wonderful example of a handwrought silver bracelet is by Harry H. Begay and is available from Chacadog.com – it is not cheap but the quality of the workmanship and materials deserve no less.

Alternatives in Blue:  Blue is an extremely popular colour for gemstones and there are a range of other gems in blue or blue-green.  For transparent gems, we suggest blue topaz, blue zircon or aquamarine.  Although sapphire from our mine tends to be more saturated in colour, it is possible to buy sapphire in these sky-blue shades as well.  While topaz and zircon are reasonably affordable, you will pay quite a bit more for sapphire or for aquamarine of good (not washed-out) colour.  Blue alternatives in opaque gems might include chrysocolla, agate, lapis lazuli and other similar stones.

Links of Interest:

Hope you enjoyed this article on turquoise – stay tuned for the next gem of the month.

cheers from Aussie Sapphire

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