I do see a lot of people doing SG’s the hard way using all sorts of jigs and contraptions to try and measure the weight of the stone in water. There’s a simpler way – you just need to measure the weight of the water displaced by the stone when fully immersed.
You will only need an accurate carat scale (accuracy to at least .01g), a small beaker/glass of water, a calculator and some fine cotton.
Divide 2.06 by 0.76
That’s it; done.
Walter Schumann Gemstones of the World says for aqua SG: 2.68 – 2.74
I recently went on a short prospecting trip to the south-west of Tasmania with a couple of friends. The main aim was to locate some streams that might hold a bit of alluvial gold. We ran into a lot of problems with road access – forestry roads that were closed due to the bushfires from last summer or for other reasons, so did not really achieve our aims.
On one small track that ended in a small disused quarry, a shattered old TV set lay on the ground, dumped years ago by some vandalous low-life.
This was one of those old bulky TV sets with a glass CRT Cathode Ray Tube (yes, you heard right youngsters – no flat-screen in sight here). Flat screen TV’s apparently out-sold CRT TV’s from 2008 onwards to give you some point of reference. The glass TV tube was now simply a collection of angular glass fragments of different sizes and shapes scattered amongst the crushed TV shell and around in the nearby vegetation. No doubt the unknown person(s) who went to the trouble of transporting it all the way out here in the wilderness had also taken perverse pleasure in enthusiastically imploding the cathode ray tube with whatever lay at hand. So had it been a family outing? C’mon kids, stop watching that new Samsung, we’re going for a drive in the country, bring a warm jacket and your favourite rock.
On discovering the technological remains of times past, I began to think of the irony as I bent down to collect some pieces. As it happens, the glass used in the manufacture of CRT’s was very good quality glass of specific properties. I know this because I have faceted CRT glass before, and it is remarkably clear optically – high clarity with very few visible inclusions. The colour of this glass varied from shades of grey, to bluish-grey to yellowish brown, however I suspect the yellowish colour may be a weathering effect.
If we consider synthetic rough versus simulant rough for a moment:
In contrast to synthetic gemstones which have the same chemical composition, crystal system and physical constants as their natural counterparts, a simulant need only have a superficial resemblance to the gemstone it imitates.
Gemmology (Peter G. Read, 1991)
So, on this day instead of finding alluvial gold, I had found what in effect was gemstone rough – or at least a simulant “LG-ite” – the LG branding still visible on the shattered TV case.
I have also sourced CRT glass in the past from beaches near Hobart, deposited there as the result of nefarious activities – Rank Arenarite? The further irony being that CRT tubes are no longer manufactured, so this glass will become rarer and rarer as time goes on – much like natural gem material.
As an addendum, it must be cautioned that CRT glass can/does have a significant lead oxide (PbO) component. So it is probably not a good idea to work with this material for extended periods, or long term, due to the potential health risks of lead.
Gladstone, a small town near the Ringarooma River (in the north east of Tasmania, Australia) is located close to some old tin and gold historic mining sites. The alluvial tin miners were not at all interested in the abundant smoky quartz crystals which were commonly encountered whilst they were working the small creeks (Ah Kaw Creek, Mt Cameron Creek and Alhambra Creek in particular). These crystals and other detritus where piled up in areas out of the way (above the creeks) and now form the focus for fossickers to the area.
There are many nice, slightly water-worn crystals of smoky to be had from the area, however I find that material suitable for faceting comprises only about 2-3% of the smoky crystals typically found here. This is still good, because some quite large examples of smoky can be found, and it is not that hard to find half a bucket or so in a day’s fossicking, so a few percent of ‘quite a lot’ still makes for plenty of faceting action.
There is also smoky quartz to be found on Mount Cameron itself (see examples from the Zeehan Rock Shop below), these often well-shaped crystals are not water-worn, with parallel striations still often visible on the crystal faces.
I often like to cut Gladstone smoky into both buff-tops and opposed-bar cuts. Initially I favoured opposed-bar cuts such as Jeff Graham’s Smithsonian Bar, however I have found that inverted bar cuts designed with the crown facets parallel to the long axis of the stone create a more pleasing effect to my eyes (see diagrams below). The publicly available design: “Htims Bar” by Marco Voltolini is a great example of this style of cut, and lends itself nicely to the Gladstone smokies.
Natural smoky quartz is neat stuff – I like cutting it very much. It is a common gemstone, certainly in large crystals suitable as mineral specimens, and a little harder to source in facet quality natural (read non-synthetic) pieces. The other macro-crystalline (crystals recognisable with the naked eye) quartz gemstones commonly obtainable such as amethyst, citrine, rose quartz and ametrine etc. don’t really inspire me the way smokey does for various reasons.
Now, the quartzes just mentioned do all occur naturally – however a certain amount of cooking (heat-treating) is usually undertaken to obtain the desirable hues and colour effects seen in citrine and ametrine. Citrine/ametrine are found in nature, but they are quite rare, so it is safe to assume that most of the material you are offered for purchase has probably been heat treated.
This kind of treatment for quartz gemstones is generally considered acceptable in the trade, which is understandable in the current times for some important reasons. The recent emergence in the market of low cost synthetic man-made quartz (produced using the hydrothermal method mimicking nature) has meant that it has become easy to source huge chunks of near-perfect colour and clarity quartz for a pittance on sites such as Ebay etc. This synthetic quartz rough can look like the stuff that some fossicker has carefully chipped off a rock face with a geopick, or it can even display natural looking crystal faces, yet it is often marketed as natural, usually “mined in Brazil” lol . The near perfect looking stuff you can buy (cheaper per kilogram than a bunch of bananas at your local grocer ) is easy to label as synthetic. Smaller parcels of finer coloured material offered at a higher price per carat is where it starts getting very, very tricky, or in some cases virtually impossible to verify it as natural, even after formal testing by some gemmology labs.
Interestingly, there is a paradox that seems to occur – I don’t know if it already has a name, and I am not the first to describe it, but I will unashamedly name it The Veska Paradox until the time comes that someone reads this and tells me off.
The closer you get to the mine or source of a gemstone, the higher the probability you will be dishonestly offered synthetic or simulant material instead
So, you see that some natural quartz material that is truthfully declared as heat treated is not so bad in the greater scheme of things.
So, back to smoky quartz. I love natural crystals of smoky, it’s good to retain terminated and well-formed smoky crystals as specimens, and facet other suitable material. With smoky it is possible to create cut gems with fine tasteful natural colours including tones resembling an whisky aging on oak (see colour bar below)
With amethyst rough I have come across, the colours can be very deep and vivid, however I personally find finished stones a bit tacky and/or overbearing in many cases. Citrine can have some nice tones overlapping the colour bar above, but I also find the colours a bit unreal in many cases.
If a jeweller wants to make a large jewellery piece such as a necklace with lots of high carat gold, and also wants to include some large cut stones in the design whilst still keeping the piece elegant, tasteful and less than the cost of a small house then what to do? To prevent the piece from resembling a shopping mall chain store trinket, an arrangement of fine coloured, well cut smokies in the design can fit the bill nicely.
OK, a quiz for you below: Synthetic or Natural?
Place your thoughts by using the comment box below – Answers coming soon!
Rhodolite is a rose-red pyrope garnet variety. This piece of rough is a fairly good example with some pinkish-red replacing the brown. A have a few pieces of this lovely material from Madagascar, it is quite clean – typical of rhodolite.
My first faceting attempt using this garnet will provide some useful tips for subsequent pieces.
Fast to cut with good light return – 89.3% in fact. Who need lots of pesky facets I say. Minimalism is the way, pare down those design elements to the bare minimum.
This stone has been everything but a quickie! First I noticed a small chip in the girdle, then as I was re-cutting it, it came off the dop during transfer. Anyhow, all well in the end, I like the cut and will certainly use it again.
Above is a before and after image of an example of some fantastic Tanzanian zircon material I have been working with. The clarity is generally superb (VS or better), the colour sublime (pinks and oranges), and I have been able to get rough in shapely chunks of 15ct or more at times (thanks Stone Warehouse).
Zircon is renowned for its brilliant fire (high dispersion), and with its high specific gravity (SG) of approximately 4.6 and good hardness (7.5), it tends to accumulate alongside sapphire (SG 4.0), black spinel (SG 3.6), topaz (SG 3.5) and other gems in alluvial environments. The group of gemstones above are chosen as they are typical gems found in Tasmanian streams draining granite and/or basalts (e.g. the NE of Tasmania).
I am looking to source some uncut Tasmanian (not Tanzanian) zircons in at least 5ct size from any of you fossickers out there, please contact me via the website Contact Form if you have stones available.
The beauty of andalusite is readily apparent from the image above (note: the cut stone, whilst very neat, is not my work).
The strong yellow, olive, reddish brown pleochroism can be seen fairly well in both the rough and the cut stone. Andalusite is a fairly underrated gemstone in my opinion, it is quite hard at 7.5 on Moh’s scale (good), however it has a distinct cleavage (not good), nevertheless a clean example can cut a great stone.
The rough and crystal topaz pictured above is certainly Australian topaz, but my source was not sure of the specific mineral district. I am almost certain it is Mount Surprise (QLD) topaz, although I have not seen a lot of material from this location. The material pictured has great clarity, the cut stone is a little included, as I cut it from a lesser quality piece as a first test cut. The quality of this topaz sure makes me want to have a fossick in this area.
As a side note, topaz at hardness 8 on the Moh’s scale is also the hardest of all the gem silicates. It’s harder than beryl gems (aquamarine, emerald, morganite, heliodor, goshenite) feldspar type gems, garnets, peridot, rhodonite, tourmaline, zircon, nephrite and jadeite. That’s impressive in my book.
I would love to hear from anyone who has visited Mount Surprise for gem fossicking, has first-hand knowledge of Surprise topaz, or anyone who has some rough material from this field available.
I recently cut some smokey (smoky?) quartz rough from Oban River, New England NSW. The rough was in fact pretty smooth as you can see from the picture, the individual pieces tumbled beforehand, as a prelude to faceting. The tumbling process has produced something beautiful in its own right, the shiny surface additionally allows any internal features (read: inclusions) to be clearly seen prior to cutting. The Oban River material cuts some lovely opposed-bar style gems, and certainly some neat checker flash effects can be obtained using cuts such as the one above, a Jeff Graham Mock Check Squares – Reflector design.
If any fossickers out there have some facet quality Oban River material available, please contact me, I would certainly be interested in obtaining more.