Countdown to Tucson: Opal

[PinkDiamond]

Much thanks to Robert James for the mention of our site in the ISG newsletter.


a publication of the International School of Gemology 20 January 2017



We continue our Countdown to Tucson with one of the most amazing gemstones in the world: Opal. Stop for a minute and look at the opal in the banner above. Certainly not the traditional opal that first comes to mind, but the Tucson Gem Shows offer the largest gathering of opal dealers who carry the most diverse types of opal in the world. We will talk about this one in just a bit, but first let's review what makes an opal, an opal.

The "play of color" that makes opal famous is due to silicon nodules lining up to create a "diffraction grating", which causes ambient light to be split into its spectral colors, just like a rainbow. Above you see a graphic to demonstrate how this works. This is the same concept on which diffraction grating spectroscopes are built.



An easy demonstration of this is looking at the surface of an ordinary CD or DVD disk. The structure of these disks create the same diffraction grating that breaks light up into its spectral colors.

While this may seem like a very elementary level demonstration of how an opal creates its colors, it is still a great way to understand exactly what is going on inside an opal that allows it to present the amazing colors we see.

The end result is seen below.



Precious Opal

At left you see the classic, precious opal gemstone that can be found in many locations around the world. Australia and Brazil are known as some of the finest sources, with Australia being the industry leader in diversity and volume of resources.

One of my favorite dealers in Australian opal is Rod Griffin Opals at the AGTA Gemfair 2017 show booth 1318, considered one of the most knowledgable experts in Australian Opal.



Koroit Boulder Opal

One of the most important reasons to visit the Tucson Gem Shows is that you can meet, and work directly with, the people who mine gemstones. The GJX is host to an industry leader in Koroit boulder opal who both mines and cuts these amazing gemstones: Gene McDevitt.

At left you see two large pieces of rough Koroit Boulder Opal from Gene's both at GJX that he provided to the ISG Student Reference Collection for our course study. These are beautiful examples of this truly unique Australian opal that is in high demand around the world. Below is why...



Gene not only mines this opal, he also is a master opal cutter and produces some of the finest quality Koroit Boulder Opal gemstones in the world.

At left is one of his finished Koroit Boulder Opal gemstones from our ISG Student Reference Collection. The intricacies of this material make each opal rare and unique.

You will find Gene McDevitt at GJX Booth 105. Or click* on the Koroit Boulder Opal at left to visit his website and learn more about this outstanding member of the ISG Global Network.
*Here's the link https://www.koroit.com/koroit.com/Home.html



Leopard Opal

Because opal can form in any void filled with water, many different opal formations can be found at the Tucson Gem Shows. One year I found a dealer from Mexico selling the Leopard Opal which formed in voids in basaltic rock as seen at left. This beautiful and unusual opal was seen in good supply one year at the GJX Show, and virtually impossible to find the next year. You should be aware that sometimes new gemstone materials can be found at the Tucson Gem Shows one year, and the demand and marketing make them far more rare and valuable (and hard to find) the next year. So be prepared to take a leap of faith when buying. You never know when a little known but affordable gemstone can turn into a serious investment for your store or gem dealing office.



Ethiopian Opal

Also known as hydrophane opal due to its ability to quickly soak up water, this opal has been criticized by many in the market for being too brittle to wear. However, due to the cheap nature of some of the rough it is no doubt that some cutters trying to go for the cheapest rough will produce problematic finished gemstones. There is good quality Ethiopian opal rough to be found at Tucson and a knowledgeable buyer or cutter can find viable material that produces a beautiful and stable end product.

At left you see a group of Ethiopian opal rough around a finished gemstone. As always, opal is difficult to photograph because the very nature of the gemstone requires a movement of light to create the play of color.

There is more to this Ethiopian opal than many realize. Below you see a set of images from inside an Ethiopian opal sent to the ISG by one of our graduates, Alicia Taylor, RG (known on our ISG forums as Crystal Star) that demonstrates just how remarkable this material can be.



I have read that the feature you see at left is due to fragments of ferns in the ancient formation locations of Ethiopian opals. When I took these images I had not read this and the first thing that came to mind was...fern leaves.

Perhaps someone out there has more information to share with us on this topic, but certainly the images at left and below demonstrate very fern-like features inside these Ethiopian opals.

What a great sales presentation that will make!

The images at left and below are untouched for color or anything else. These are the actual inclusions inside Ethiopian opals sent to us for evaluation.

A beautiful example of just how diverse opals can be.





My final image is a 17 year old picture I took on my first trip to the Tucson Gem Shows in 2000. This is a 6-rayed star opal. I was using an old Sony Mavica so the quality is not great, but the colors and star are exactly as seen in person.

No other gemstone will offer you the diversity and potential profits quite like opals. And no other place in the world will offer you the diversity of opal types and dealers like the Tucson Gem Shows.

If you would like to learn more about opals from some great experts, visit the OpalholicsAnonymous.com website to meet some friendly folks who love to share a wealth of knowledge about opals.

We look forward to seeing you in Tucson. Stop by our Booth at the AGTA Gemfair Tools and Technology Show Booth 2209.

More Countdown to Tucson 2017 is yet to come in the days leading up to the Tucson Gem Shows.

Robert James FGA, GG
President, International School of Gemology

To learn more about our world-class programs in gemology and jewelry appraisal, visit the ISG.

ISG | ISG@SchoolofGemology.com | International School of Gemology | PO Box 1727 | Helotes, TX 78023

©2017 International School of Gemology. ALL RIGHTS RESERVED. We encourage sharing and caring throughout the industry as long as all copyrights are left intact.

[SwordfishMining]

The new Imperial Chrysophrase coming out of Central Australia. I went for the lightest stuff not the greenest. Although I got a few pieces of that too you could see into an inch or more. I thought the Gem silica color would be worth more when done up right than the green green.

[Lydia]

That is really pretty. I think you made the right choice.

[kjsspot]

What plans do you have for that John?

[Brightlights]

The new Imperial Chrysophrase coming out of Central Australia. I went for the lightest stuff not the greenest. Although I got a few pieces of that too you could see into an inch or more. I thought the Gem silica color would be worth more when done up right than the green green.

IMG_1484870801746.jpg

Curious John, what's the going rate in the chrysophrase?

[SwordfishMining]

I got it for .18 a gm pick retail. 80 a pound. I really dont know what others sell it for still LOL. They had a necklace sell 13mm beads with 3 gold and sapphire accent beads for 60k online while they were there. From what I saw for sale online the transparency is the biggest factor to raise the price next to the mine and none was this good uncut. I plan on keeping a couple for looking at, sell some slabs and cab some to sell. .40 a gram for the lessor ones at least to make it worth my time to Scott who wanted in on the pick. He gets to pick out of mine for that too. Slabs probably at 1.50 a gm. We'll see when we get around to it what Gem silica cabs are going for per ct.

[Brightlights]

John,

Thanks for the heads up on that chrysphrase. I've got some oldstock and didn't know what it goes for. I've got a nice big silver ring I think I'm gonna cab a piece for.

[SwordfishMining]

They said what I picked usually is found in the high grade crate at 200 a pound so I could mark it up to that no problem. He cuts the best himself and sells cabs.

[Artfldgr]

Actually its not a diffraction grating in opals. in opals its photonic crystals, which is a completely different property.
diffraction gratings cant produce some of the effects. they CAN divide light at an angle due to lights wavlengths being different sizes and the angle.

Photonic Crystals on the other hand are blocks or arrays of very uniform in size spheres (in the case of opal its silica or is it silicate? or both)
the spheres are packed in uniformly as well, and water is a medium between them.

Wiki even uses an opal in a ring as an example of the optical properties.

A photonic crystal is a periodic optical nanostructure that affects the motion of photons in much the same way that ionic lattices affect electrons in solids. Photonic crystals occur in nature in the form of structural coloration—and, in different forms, promise to be useful in a range of applications.

In 1887 the English physicist Lord Rayleigh experimented with periodic multi-layer dielectric stacks, showing they had a photonic band-gap in one dimension. Research interest grew with work in 1987 by Yablonovitch and John on periodic optical structures with more than one dimension—now called photonic crystals.

Photonic crystals can be fabricated for one, two, or three dimensions. One-dimensional photonic crystals can be made of layers deposited or stuck together. Two-dimensional ones can be made by photolithography, or by drilling holes in a suitable substrate. Fabrication methods for three-dimensional ones include drilling under different angles, stacking multiple 2-D layers on top of each other, direct laser writing, or, for example, instigating self-assembly of spheres in a matrix and dissolving the spheres.

Photonic crystals can, in principle, find uses wherever light must be manipulated. Existing applications include thin-film optics with coatings for lenses. Two-dimensional photonic-crystal fibers are used in nonlinear devices and to guide exotic wavelengths. Three-dimensional crystals may one day be used in optical computers. Three-dimensional photonic crystals may also provide a source of power for our electronics, thus cutting down the need for an electrical input for power.

this property has been exploited all over... in nature and the lab
small holes in fiber optics the length of the fiber makes a photonic crystal that helps guide light and improve coherence over a long distance


in the lab they often make them with a lattice structure in resin where each line is created by a UV laser that hardens the resin in its path
they turn it on and off and move it to create the arry, then they drain the liquid, and what remains is a photonic crystal of a different sort



this is what opals look like inside


here are man made structures copying opals


where diffraction patterns reflect light, photonic crystals guide light
and in some case you can get them to lase

[Artfldgr]

Actually there are lots of effects that appear the same but the underlying physics is different
and some of it is in gemstones ranging from double images, to all manner of oddities
which kind of why people like to wear them and put dull ones around bushes.