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Gem of the Month Archive

Gem of the Month: Carnelian

Posted July 16, 2007 By AussieSapphire

carnelian.jpgThe July birthstone is well known as Ruby but for those looking for an unusual alternative, the ancient gem Carnelian may be of interest. 

(Image from OldenWisdom)

Gemmology Matters:  Carnelian is a cryptocrystalline form of quartz and is a translucent, semiprecious variety of chalcedony that owes its red to reddish brown colour to the presence of dispersed hematite (iron oxide) within the silica mineral.  As with other varieties of chalcedony, hardness is 7 on the Moh’s scale.  The stone is closely related to Sard which is a brownish colour – see here for more information.

Most commercially available carnelian has undergone some enhancement treatment.  Yellow/brown chalcedony has been routinely heat treated at low temperatures to create red carnelian stones for many centuries.  Carnelian is mostly cabbed or formed into beads and is an inexpensive stone with warm and attractive colour.

Mythology and Lore:  Carnelian has been valued for many centuries and is mentioned as a birthstone in ancient Arabic, Herbrew and Roman tables.  The stone is named after the Latin word “carneus” for “flesh” because of its reddish colour. 

As a healing stone, carnelian may be used to treat blood disorders, menstrual problems and back pain.  Continuing with the theme, carnelian has been thought to help with infertility and may be worn to enhance passion.  Carnelian is associated with the zodiac signs of Leo and Virgo.

Carnelian seal ring - copyright VRomaLike other forms of chalcedony, carnelian is well suited to intaglio work, engraving/carving and for seals.  This fine example of a seal ring depicts an actor holding a tragic mask and is held in the British Museum (image from VRoma, copyright Barbara McManus 1999)

carneliangem.jpgThis second example is a carnelian carved gem inscribed in Greek – this one is from Hixenbaugh Ancient Art and may be purchased through their website if you would like to own a piece of history from Ancient Greece.

Alternatives in Orange/Red: Obviously the king of red gems is Ruby but there are many other alternatives in red.  For transparent gems, red spinel is increasingly popular and some species of garnet provide a range of colours from red to orange.  Carnelian is generally more translucent than these alternatives and does have a “waxy” look that is quite distinctive. Carnelian with its affordability and warm colour should give collectors a reason to have at least one example of this ancient gemstone.

Links of Interest:

Unforunately, we have no carnelian listed online although we do have some small cabochon carnelian in stock – if you want reddish orange, we also suggest some natural colour zircon. Both gems are very affordable so why not get some of each.

Cheers for now from Andrew and Leah Lane (Aussie Sapphire).

More on Garnet

Posted January 7, 2007 By AussieSapphire

The birthstone for January is generally acknowledged to be Garnet. Unlike some other months, there are few alternative stones for January although some sources list emerald as the “mystical stone” for January.  However, garnet is a very versatile gemstone in its own right with a beautiful range of colours available.

tsavorite_suite.jpgSince we have already covered Garnet in our usual “Gem of the Month” format, we will explore some of the varieties of garnet in this month’s article.  An example of one of the more unusual varieties is tsavorite seen in the photo at left from Palagems in their Tsavorite Buying Guide.

Garnet is a group of minerals with similar chemical composition, physical properties and crystal structure.  There are six species of garnets recognised although many gems lie on a substitution scale between species making a positive identification somewhat challenging in many cases.  See the Garnet Factsheet on Mineral Miners for more discussion on garnet species and how to distinguish them.

  • ALMANDINE:  Colour is typically a deep, rich red – less valuable specimens have more brown.  Sources:  Brazil, India, Madagascar, Sri Lanka, U.S. in Arizona, Idaho, New Mexico, Utah, Arkansas and Kentucky.
  • PYROPE:  Colour is usually deep, rich red or variations on this.  Sources:  Australia, Czechoslovakia, South Africa – Zimbabwe and Mozambique.
  • SPESSARTITE:  Colour is ideally bright orange but ranges from reddish orange, red, reddish brown, to brown.  Sources:  Brazil, Namibia, Pakistan, Sri Lanka, US.
  • ANDRADITE:  Colour usually ranges from green, yellowish green to greenish brown and may occur in black.  This species includes the highly sought after demantoid garnets.
  • GROSSULAR:  This species ranges widely in colour from colourless to black with almost all colours in between (red, green, pink, yellow, etc).  This species includes the rare and valuable tsavorite garnets.
  • UVAROVITE: This quite rare species of garnet is dark green and often found as fine crystal clusters (sometimes referred to as drusy because of the small crystal formations).

For more reading on this, I recommend the Garnet page on the Gemology Project – this is a new resource associated with the Gemology Online forum so it is highly recommended for anyone interested in gems.

Due to the complexity of the garnet group, there are quite a number of individually named gem varieties.  Here are just a few:

  • HESSONITE: this garnet falls into the grossular species and occurs in yellow, orange and brownish colours.
  • RHODOLITE: This rose-red to purple garnet is part-way between Almandine and Pyrope – closer to pyrope than the Mozambique type garnet which is also a pyrope-almandine garnet of a deep red shade.
  • TSAVORITE: Medium, intense green to slightly yellowish green.  This rare and valuable gem is found in Kenya around the Tsavo National Park area for which it is named.
  • DEMANTOID:  Another highly sought after gem – the best examples will show intense green colour and “horsetail” inclusions.

The commonly found red garnet (likely of pyrope-almandine type) are very affordable and used in jewellery all around the world.  A range of these in calbrated sizes are available in our online shop for those looking to use them in jewellery at the more budget end of the scale.  A little higher up the scale is rhodolite and spessartite.  Spessartite in particular is becoming very popular and with a current shortage of rough, they are certainly not a cheap option.  For those who want only the best, we suggest you consider the more rare varieties of garnet such as demantoid, tsavorite or colour change garnets (including the new blue varieties from Madagascar).

demg107.jpg A classic example of a demantoid garnet from the Ural Mountains in Russia – clean except for the diagnostic “horsetail inclusions” and available from Mineral Miners.

spess-b.jpgThe picture at right shows some spessartite cabochon cut from rough we sourced from Nigeria.  We have spessartite rough available online now and we hope to list some of our faceted and cabbed gems as soon as possible.  These gems can show some real fire and make fantastic pieces of jewellery.

I hope this article has inspired you to consider garnet for your next gemstone purchase – there is certainly something for everyone in this fantastic range of gems.

Gem of the Month: Turquoise

Posted December 11, 2006 By AussieSapphire

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

Gem of the Month – Yellow Topaz

Posted November 12, 2006 By AussieSapphire

imperial.jpgYellow topaz is also known as the modern birthstone for November.  Although now probably overtaken by the more commonly used Citrine, Topaz is a particularly lovely gemstone which is deserving of more recognition in its “precious” form.

Photo at left from is a good example of Imperial Topaz from Mineral and Gemstone Kingdom

Gemmology Matters:  Natural Topaz is a fluro silicate with the chemical formula Al2SiO4(F,OH)2 .  It is found in a variety of colors including brown, red, orange, pink, sherry, yellow as well as colourless.  Often the shades from yellow through to red are termed “Precious Topaz” with particular colour combinations described as “Imperial Topaz” – those gems denoted as Imperial and the very rare red varieties command the highest prices. The definition of Imperial Topaz colour (reddish-orange?) can be quite complicated – see this Gemology Online thread for more discussion on this subject. 

sherry_topaz.jpg This example of a sherry coloured topaz crystal is from John Betts Fine Minerals (Gem Crystals catalogue) – this specimen is from Pakistan and shows the hexagonal crystal habit of topaz very clearly.

Green and blue topaz are naturally very pale, the very bright colours often found in jewellery today are the result in irradiation treatment – Sky Blue, Swiss Blue and London Blue are names used by the gem trade to refer to the depth of color.  See our Blue Topaz article for more information.  Please note that surface colour coatings are becoming more common in Topaz – starting with the multi-colour version of Mystic Topaz, but now also used to create other colours such as pink.  Gems treated in this way should be treated with care to avoid damaging the colour coating.  These types of gems should be far cheaper than naturally coloured stones so be wary when purchasing brightly coloured Topaz and ask about enhancement treatments first.

The principal sources for topaz is Brazil – also found in Sri Lanka, Russia, Australia, Africa, Mexico and Pakistan.  Topaz is an excellent gemstone for jewellery with a hardness of 8 – although it has perfect cleavage which may present some danger when setting in jewellery.  For this reason, topaz should be treated with care and protected from hard knocks.

Mythology and Lore:  While the blue variety of topaz is for those born in December, yellow topaz is the modern November birthstone.  Topaz may be given to celebrate the 4th, 19th and 23rd wedding anniversaries.

Most of the mythology for topaz relates to the yellow variety as natural blue topaz is quite rare and pale in colour.  The Egyptians believed that topaz was coloured with the golden glow of Ra – the sun god.  The importance of Ra made topaz a very powerful protective amulet for the faithful.  This link with the sun was also found in ancient Roman culture where topaz was associated Jupiter, also a God of the Sun.

Topaz was once thought to strengthen the mind, increase wisdom, and prevent mental disorders.  It was also thought to guard against sudden death.  Legend says that topaz has the power to dispel all enchantment and help improve eyesight. The ancient Greeks used the gem to increase strength and make its wearer invisible in times of crisis.  Used in medicine in ancient time, topaz was said to cure insomnia, asthma, and hemorrhages.

imperial-topaz.jpgThis imperial topaz photograph is from the Palagems Topaz Buying Guide which also has some excellent information on the famous Ouro Preto mine in Brazil (see link below).

Alternatives in Yellow:  The range of colour in Precious Topaz brings to mind the amber gold of fine cognac, the blush of a ripe peach and all the colours of a setting sun.  While its cheaper cousin, Citrine, is commonly used these days and is an alternative November birthstone, it is slightly softer and does not have quite the complexity of colour that is present in a particularly fine Topaz.  Sapphire is also found in yellow – while beryllium treated yellows now abound in the marketplace, a fine golden yellow sapphire of natural colour can command very high prices.

Links of Interest:

Aussie Sapphire does not currently have any topaz in stock – we do have a small supply of good yellow sapphire (natural and basic heat only – no beryllium treatment).  None of this is currently listed but we invite you to contact us directly if you are interested.

cheers for now from Aussie Sapphire

Gem of the Month: Tourmaline

Posted October 15, 2006 By AussieSapphire

tourmaline-icga.jpgThe theme for October birthstones is colour and lots of it!  We have already covered Opal with its “play of colour” in a previous article.  This time, we look at the alternative birthstone for October: tourmaline – the Rainbow Stone.  (Photo from ICGA article)

Gemmology Matters:  Tourmaline is truly a fascinating gemstone. Tourmaline is a very complex group of minerals but may be described as a complex aluminium borosilicate where colour is caused by presence or absence of various metal ions (Fe, Mn, Cr, V, Ti and Cu) in the crystal structure.  Hardness is 7 to 7.5 on the Moh Scale making it suitable for most jewellery applications.  Commonly found as prismatic crystals (trigonal-hexagonal), often with vertical striations along the prism faces.

While it can have fantastic colour, strong dichroism and sometimes unstable crystal structure means that tourmaline can be quite challenging for the gem cutter. Cutting orientation is very important so that the faceted gem displays the best colour possible.  Where the colour is too dark looking through the crystal (referred to as “closed C-axis”), they may be cut in elongated shapes (where the A-B axis shows better colour).  Some types can be unstable during the cutting process – if not handled carefully, the stone can crack badly while being faceted.

A fascinating property of some types of tourmaline has led to it being used for scientific and industrial purposes.  The piezoelectricity effect occurs when an electrical charge is induced by applying pressure to a tourmaline crystal in the direction of the vertical crystal axis – this can be used in pressure measuring equipment and other scientific applications.  A similar effect called pyroelectricity occurs when the crystal is heated yielding a positive charge at one end of the crystal and a negative charge at the other.

Tourmalines are mined everywhere in the world with important commercial deposits located in Brazil and parts of Africa.  Other notable locations include Sri Lanka, Madagascar, Pakistan, Afghanistan and the USA. The price range for gem quality Tourmaline varies almost as much as its colour with some rare and sought after varieties bringing extremely high prices.  The recently discovered Paraiba source in Brazil with its intense neon blue coloured stones produces gems that are particularly sought after.

mixed_tourmalines.jpg325g-tourm-sm.jpgThese photos show a small selection of mixed colour tourmaline from Nigeria.  Dont have much of this material left now so keep your eye on our online shop for the last few bits.

Mythology and Lore:  Tourmaline is known as the “Rainbow Stone” from an ancient Egyptian legend: on the long way from the Earth’s heart up towards the sun, Tourmaline travelled along a rainbow, collecting all the colours of the rainbow on its journey.  The name derives from the Sinhalese (Ceylon) word “tura mali” meaning stone of mixed colours. 

The Empress Dowager Tz’u Hsi, the last Empress of China, was a great collector of pink tourmaline and rubellite.  She imported tons of tourmaline from Southern California in the early twentieth century, creating a gem rush in San Diego during the period.  She loved pink tourmaline so much that she was laid to rest on a pillow carved from this gemstone. 

Tourmaline is the birthstone for the month of October and is associated with the zodiac sign of Libra.  Legend says tourmaline inspires artistic expression, enhances intuition, increase self-confidence and amplify one’s psychic energies.  Tourmaline may be used to neutralize negative energies, dispel fear and grief, and to aid in concentration and communication.

Alternatives in Multicolour:  Tourmaline is unique for its range of colours and gems where more than one colour is displayed.  While tourmaline may be found in many colours which are also represented by other gems, it is the bi- and multi-coloured varieties which are difficult to find elsewhere in the gem world.  Sapphires may show this bi-colour character (called “parti” in Australia) but generally the colours tend toward the blue-green-yellow and do not display the sharp boundaries of significantly different colours seen in some tourmaline.

Links of Interest: 

Hope you enjoyed this article on Tourmaline – truly worthy of a book but we’ll leave that job to someone else.  We still have some nice pieces of tourmaline rough in stock as well as some nice cut gems in a variety of colours (including nice emerald greens and intense pinks). Please enquire at any time about these. 

Cheers for now from Aussie Sapphire