Tasmanian Weld River rough

Tasmanian Weld River alluvial gemstones

I recently received the above collection of nice gemstone rough from a forum member on Tas-Prospecting – the member had fossicked these stones from the Weld River in Tasmania’s NE. The parcel contains a large smokey quartz, several water-worn rounded topaz crystals (approximately 3 – 4ct size each) and some sapphires. I am selecting and cutting any suitable stones for him. The front-most sapphire (around 2.2ct size) has a lovely blue tone as you can see below.

Weld River sapphire

A geological interlude…

Corundum is widespread in Tasmania, mostly in the form of small sapphire grains in alluvial deposits. These are probably related to the occurrence of similar material throughout eastern Australia and South East Asia. The sapphire is thought to have been formed in syenite or similar rocks at great depth, and rapidly brought to the surface in pyroclastic eruptions of alkaline basalts, which are usually closely spatially associated.

Above extracted from Bottrill (1996) Corundum and Sapphire in Tasmania Tasmanian Geological Survey Record 1996/05

So, in a nutshell, the sapphires found in Weld River have been eroded out of the Tertiary alkaline basalts common in the local area, then concentrated in the small streams draining these basalts. The Tertiary alkaline basalts are the same rocks that weather to form the rich red-brown soils in the Scottsdale area, so productive for crops etc. These basalts in effect provided the transport mechanism for the sapphires, from their point of creation deep within the earth’s crust, to nearer the surface.

I will begin by cutting two topaz pieces – the piece on the right in the photo below has a slight aqua tone to it. Since both stones are relatively small, I will choose designs with fewer facets, but go for good light return.

2 x topaz: Dopped and ready
This cut is a good option: Morph Square – Relector.

Ok, smaller topaz on the right: Morph Square – Reflector. The topaz on the left will be a cushion cut (see below).

Jeff Graham Quick Cushion
1. Pavilion going in
2. Still a bit rough
3. Shape looking good now
Pre-polish with #3000 diamond powder on a tin lap
This is the cushion cut topaz (pavilion) getting started. A bit of rough loss to one side. Have gone a bit further with the pav to eradicate most of the visible inclusions you can see.
Looking pretty good, pavilion complete.

Also starting to have a look at the large ~ 32ct smokey quartz crystal for cutting purposes. Most of the stone has pretty good clarity, however a cloudy section will need to be trimmed (see below).

Smokey quartz crystal showing approximate trim line

This smokey will make a lovely opposed bar cut gem, it has a very nice colour tone. Since the final length to width ratio of the rough will be about 1.50, the Jeff Graham Opposed Bar cut will fit the bill, if the ratio had been closer to 2.0, I might have cut it as a Marco Voltolini Htims Bar.

The two sets of parallel facets perpendicular to one another – one on the crown, and the other on the pavilion combine to make an attractive, flashy checkered effect in the cut below.

Jeff Graham Opposed Bar cut

 

Clarity after trimming
Profile view – fits the proposed cut quite well
Dopped and ready

OK, back to the topaz. Ready to transfer cushion topaz in order to cut the crown.

Ready for transfer, test alignment.
5 minute epoxy
epoxy and post-it notes
epoxy-filler: to make epoxy thicker and a better glue strength
Transfer, flip over in a second to pool the epoxy in the opposite direction
Crown 1 (C1)
Crown 2 (C2)
Crown 3 and 4 going in
Table facet going in
That’s a wrap, happy with the result – looks for all purposes like a diamond! Will get a close up shot next. The Cushion-cut rocks.

Back to topaz number 2 (Morph Square – Reflector). Putting in the first crown facet

C1
Crown C5 in

Ready for pre-polish. (Slight interlude and back to cutting again after some urgent geology work over last few days).

Pre and final polishing went OK, and the first two topaz’s are finally done. Reflectors are notoriously hard to photograph, a slight angle seems the go, as you can see from the image below.

Topazes
cushion-cut topaz
Partners in crime

Also starting to think about a design for the sapphire pictured at the start of this post. I’m thinking perhaps a Tic – Tac (90.6% light return). The design is selected to maximise the yield of the stone. A squarish shape is going to be the best idea from examining the stone in detail.

Tic – Tac designed for higher RI materials such as garnet and sapphire etc.

Back to the smokey quartz. I have re-oriented the smokey on the dop as I felt that I would get a slightly better yield by rotating the stone by 90 degrees.

re-dopped smokey.

I am starting to prefer dopping wax rather than cyanoacrylate, much easier to remove the stone when required by applying some heat.

Cutting P1 – P4 facets
Ready to put in the pavilion bar facets
Bars are in.

The pavilion bar facets you can see above are only separated by a few degrees each, which helps to create the amazing flash effect seen when just moving the finished gem a little from side to side.

I have already pre-polished the bars (using diamond on a tin lap).

Ready for final polish
Darkside Lap (highly recommended)

The Darkside Lap above is great for final polishing using oxides for quartz and a range of other gems, I am using cerium oxide on the Darkside (with water as a lubricant) on the smokey.

Pavilion complete!
Pavilion from another angle

Ready to transfer so the crown (opposed) bars can be put in.

Transferring – to start crown
Starting crown (C2)
Crown (C3) going in
Crown (C3) in.
About to do table facet
All crown facets in.
Pre-polish
Final polish going in
Done!
Angled view. The stone has some pleasant olive and cognac overtones.
Better shot, slight inclusion(s) visible in top LH corner, but still great!

Let’s cut a sapphire now – doing the Tic – Tac cut.

Line up very carefully for dopping
Dopped with wax
Looking good and ready to go.
Just a wee dram to settle the nerves

I believe it is appropriate at this point to state that I do not condone the drinking of alcohol whilst operating a faceting machine.

Tricky…
indentation affecting size/yield
Looking good pavilion-wise. Great colour showing through during pre-polish.
Crown going in

You would not believe the fun and games I have had with this little sucker…

The end result was well worth it though, what superb colour and clarity! Lets call it the Fisherman’s Friend cut, rather than the Tic – Tac, lol.

Final result: 0.5ct  – so yield about 25%, which I am reasonably happy with given the initial shape of the rough.

Aim is to take some good photos tomorrow, then pack it all up and ship it out!

The End

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Rhodolite garnet – a quickie

Think I’ll do a Quickie..

13.87ct rhodolite garnet rough

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.

Quickie facet design by Jeff Graham

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.

Dopped and ready for some love.
We’re away!
Main pavilion facets, still a bit ragged.
Looking more even – starting to put the girdle in.
More definition now – the girdle is in.

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.

Complete – my Slowie…
The result: 2.1ct final stone, 7.7mm across the flats. The yield is understandable given the recut required.

 

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Indicolite – blue tourmaline project

Cutting exercise – blue tourmaline crystal.

Indicolite crystal above and below with its lovely ‘garden’ which will be revealed a little later in this story.

Indicolite is a rare, steely-blue coloured form of tourmaline highly prized as a gemstone. Above are two views of a piece of rough I have at hand weighing around 18ct. You can see in these pictures a bit of the blue-green dichroism typical of tourmaline exhibited by viewing the crystal in different directions.

The tourmaline piece is included, however I feel like using this as a feature – any inclusions present will hopefully provide extra interest to the stone when cut.

This interest is sometimes called the garden, a term often used when describing the rich suite of inclusions typically present in emeralds. Just in this case my garden has blue grass. If you want a stone as clear as glass, go and get a synthetic one I say, they’re real cheap, lol. I am sure the jewellery store at the local shopping mall will be able to help.

I have ground a small flat plane on one crystal edge to provide a base for securely  dopping (affixing) the stone to a small brass holder (dop) using super glue (cyanoacrylate).

Dopped and ready for some cutting action
Think I’ll use this, simple but effective..

The cut is designed to give a nice colour flash when rocked along the long-axis. I like flashes in faceted stones – it’s the light-return happening, its real purty. This cut has 90.7% light return as specified by the designer … nice. What this means in simpler terms is that of all the photons (light rays) incident on the facets of the top crown, around 90% of them are bounced back into your waiting eyes. This is a good thing. Who wants a dull stone? The astute may notice that I have oriented the stone at 90 degrees to the cutting diagram above, so my colour flash should happen when the completed stone is rocked along the short axis.

Cutting the pavilion
Messy work!
Pre-polish in progress
Pre-polish has revealed the insides
Transfer in progress
Transfer complete, let’s start the crown.

Pre-polish in progress
Pre-polish the table facet
Start the final polish
Just about done
Yeah, it’s done
Complete
A stone with some personality!

Yes, the stone is flawed. I think it is still worthwhile, attractive and of value. After all, we are all deeply-flawed human beings I say. It’s up to us to make the most of any strengths to offset any perceived weaknesses.

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Tanzanian zircon

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.

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Pleochroism – andalusite

andalusite

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.

Andalusite rough, about 40ct total.
Looks good with a black background

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