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Archive for November, 2006

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

Website Re-organisation

Posted November 4, 2006 By AussieSapphire

Just a quick note to alert our regular website visitors to a slight re-organisation of our categories.  Where our gold jewellery was once all listed together, we have split these into three new categories for Rings, Pendants and Earrings.  All of these new categories are accessible from the main Jewellery Catalogue which is a good spot to start exploring our range.

We have some fantastic new items (some in 18k white and yellow gold) in stock now with lots more to list so we definitely recommend you take a look through these catalogues.  We have chosen some of our best blue sapphire for these pieces and we are thrilled with how they turned out.

Aussie Sapphire - 18k Yellow Gold Ring with Sapphire & DiamondHere is just one example: – this 18k yellow gold ring features a 0.59 carat sapphire with 0.5 carats of diamond – four round diamonds squaring the sapphire with smaller accent diamonds channel set along the split shank.

This would make a fantastic gift for someone special – it looks fantastic !

We have more items to list and hope to do this over the next week.  More cut black spinel and a great new batch of sapphire cutting to sort through including some unheated sapphire.  Lots more to do so better get back to the grindstone – stay tuned here for more announcements.

cheers for now from Aussie Sapphire

New England Sapphire

Posted November 4, 2006 By AussieSapphire

Have just loaded up a new article we have written about Sapphire and Ruby in NSW, Australia with particular reference to New England sapphire.  The article contains a number of photos so take a look.  We welcome your feedback so feel free to leave a comment.

cheers for now from Aussie Sapphire

NSW Sapphire

Posted November 3, 2006 By AussieSapphire

The following article is one we wrote for the Corunduminium website – the updated version of this website has not launched yet so we thought we would post this article here to give it a home until then.  The purpose of the article is to discuss Australian sapphire with particular reference to the New England gemfields where our own mine is located.


SAPPHIRE AND RUBY FROM NSW, AUSTRALIA
Andrew and Leah Lane, Aussie Sapphire

Sapphire and ruby, the gem varieties of the mineral corundum is found in many east coast locations of Australia. Sapphire is found from north Queensland to north-east Tasmania and in NSW is concentrated in the highland regions along the Great Dividing Range.  Ruby is less common in Australia but may be found at various sites in NSW  notably the Gloucester area but also near Tumbarumba as well as the Macquarie and Cudgegong Rivers.

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Figure 1.  Distribution of Sapphire and Ruby in Australia (after Sutherland & Webb, 2000

SAPPHIRES

Sapphires were first discovered in Australia as early as 1851 when they were found at the Cudgegong and Macquarie Rivers during the Gold Rush period.  Sapphire was found alongside gold and tin in many highland regions during prospecting and mining activity. 

The largest and most economic sapphire deposits are in the New England region of New South Wales (NSW) around Inverell and Glen Innes, and central Queensland around Anakie and Rubyvale.  The New England gemfield is said to produce Australia’s finest blue sapphire with Queensland sapphire renowned for their range of colour (including yellow, green and parti sapphire).

figure2.jpgFigure 2.  Location of commercial deposits of sapphire in New South Wales and Queensland (click to see full size image)

 

Sapphire was not mined commercially in NSW until 1919 when a rich area on Frazers Creek near Inverell was worked by CL Smith.  This encouraged more mining in much of the sapphire bearing area of Glen Innes and Inverell which continued for 10 years until the Great Depression.  Large scale commercial mining did not resume until 1959 when prices for rough increased due to a shortage from the traditional sources in South East Asia. 

At the height of the sapphire boom in the 1970’s, there were well over 100 mining plants operating in the New England region (Mumme, 1988).  There was some consolidation of the industry during the 1980’s  in response to lower prices and exhaustion of some of the very rich alluvial sources in the area.  Market conditions have continued to be difficult resulting in a decline in mining activity within the region there are now only a very small number of commercial miners still operating.

Within the New England gemfield, sapphires typically occur in Quaternary and Tertiary alluvial deposits in both present day watercourses and fossil drainage systems. The sapphire-bearing gravel layer (or “wash”) varies in thickness and depth but may be up to a few metres thick in some palaeo-alluvial channel systems.  It is thought that most of the sapphire was derived from the weathering and erosion of volcanic ash deposits (volcaniclastic rocks) that were erupted onto the earth’s surface during early explosive phases of volcanic activity (Facer & Stewart, 1995).  These deposits were then distributed and concentrated along drainage channels. 

Within the New England region, these processes have combined to create major sapphire deposits along Reddestone Creek, Wellingrove Creek, Kings Plains Creek, Horse Gully, Frasers Creek and Swanbrook (see map).  In these areas, sapphire is commonly found in association with pleonaste (Black Spinel MgAl2O4) and zircon. 

Australian sapphires are typical of corundum formed in iron-rich alkali basalt terrains and they have similar gemmological properties to those from other such deposits found in Thailand, China and Cambodia. The colour is quite saturated compared to sapphires found in some other resources  for example the Geuda sapphire of Sri Lanka which is extremely pale before heat treatment to intensify colour.  Colour zoning is also common in Australian sapphire and may appear as hexagonal crystal growth patterns or parallel to the prism (Mumme, 1988; Sutherland and Webb, 2000).  

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Photos 1, 2 & 3.  Colour zoning in sapphire crystals from Reddestone Creek

The sapphire is also often strongly dichroic with a strong blue colour on the main axis and lighter blue or green from the other direction being common.  Sapphire from the Reddestone Creek in the New England is known for producing a higher proportion of sapphire that shows blue on both axes or blue with a greyish cross – these sapphires that possess a blue “cross table” are locally referred to as “blue on blue” and command higher prices than those with a green cross or less desirable colour.  Yellow sapphire is relatively rare in the New England resource compared to Queensland although Wellingrove Creek in particular was noted for producing some very fine yellows. 

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Photos 4 & 5. Sapphires with Blue cross table (Photo 4) and Green cross table (Photo 5)

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Photos 6, 7 & 8.  Parti colour sapphires – strong blue and light yellow zones in the 9.3 carat stone in Photo 6, a strong yellow corner in the 33 carat stone in Photo 7, and distinct yellow triangular patch in Photo 8 – all were mined on the Reddestone Creek.

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Photo 9.  Fine yellow sapphire of good size (natural and untreated) found in the Inverell district and cut by Sorn Lim of Glen Innes.

Gem quality corundum makes up only a very small proportion of all mine production with most corundum found being opaque, translucent or heavily included.  Due to the volcaniclastic nature of these minerals, size tends to be relatively small compared to some very large corundum specimens found in other locations.  Corundum specimens larger than 200 carats are rarely found in the New England gem field and gem quality sapphire above 30 carats in weight may still be found but are now considered somewhat rare.

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Photos 10 & 11.  Corundum specimens – 10 is opaque weighing 255 carats and 11 is translucent weighing 190 carats

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Photo 12.  Sapphire crystal (green cross table) weighing 85 carats, found on the Wellingrove Creek.

Sapphires often occur as tapering hexagonal pyramids and are known as dog tooth crystals.  These often show distinct colour zoning as striping along the crystal or lighter zones at the tip. Crystals may be round and smooth or may have distinct faces in a hexagonal shape.  Occasionally crystals may be found that are fused together or barrel shaped with double terminations.  The following photographs show some typical examples – all found within the Reddestone Creek within the past decade.

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Photos 13, 14 & 15.  Examples of dog tooth sapphire crystals illustrating colour zoning and crystal habit

RUBY

Ruby is less common in Australia but may be found at various sites in New South Wales, including the Macquarie and Cudgegong Rivers and the Tumbarumba area.  The major source of gem quality ruby is in the Gloucester-Barrington area, in the drainage of the ancient Barrington volcano. In this area, rubies are found in association with sapphires of various colours.  Australian rubies tend to be very small (usually less than a carat) and in most deposits are alluvial in nature (Sutherland and Webb, 2000).  Due to the rarity of ruby in Australia, there is limited large-scale mining activity.

The only commercial ruby miner in Australia is Cluff Resources Pacific (an Australian public company).  Cluff has undertaken extensive exploration within the Gloucester area and is currently producing ruby and sapphire from their mine (edited to add that this operation is not producing currently – Nov 2007).  Although only a relatively small operation, the company reports that a large resource has been mapped and production is consistent.  Interest in this operation has been relatively high, perhaps enhanced by the association with the landowner who owns the mineral rights – the Packer family of PBL (Australia’s largest diversified media company).  It is possible that investment in this project has been influenced by the association and original negotiations with the late Kerry Packer – a very successful entrepreneur well known for his business acumen.  These rubies and pink sapphires are now marketed through Ellerston Gems – named for the property where they are mined. 

CONCLUSION

New South Wales in Australia is an important source of gem quality corundum (mainly sapphire) and large areas of untested ground with encouraging inferred yield.  Improved market conditions for sapphire could easily result in a significant increase in mining activity.  Environmentally friendly production methods and a stable long term supply give the Australian sapphire industry new opportunity to market these gems.

SOURCES:

  • Facer, R and Stewart, R. (1995). Sapphires in New South Wales. Department of Mineral Resources, Sydney.
  • Mumme, I. (1988).  The World of Sapphires. Mumme Publications, Port Hacking.
  • Sutherland, FL and Webb G (2000). Gemstones & Minerals of Australia. New Holland Publishers, Sydney.
  • Sutherland, FL, et al. (2002).  The Tumbarumba Basaltic Gem Field, New South Wales: In Relation to Sapphire-Ruby Deposits of Eastern Australia.  Records of the Australian Museum 54: 215-248.

Copyright Notice:  All photographs were taken by Aussie Sapphire (A & L Lane) and are not to be used without permission.  Source of Figure 1 is aknowledged above.  All rights reserved (2006).