Ellensburg blue agate is the third-rarest gem on the planet, but that’s not to say you won’t stumble across some if you take a stroll down Ellensburg way.
Sure, the chances of your find actually being blue agate are very slim, which has led to many gem hunters heading home with nothing but the Ellensburg blues, but maybe you’re one of the lucky ones!
To find it if you just won the geo-lotto, let’s discuss how you can be sure a rock is indeed one of the infamous Ellensburg blue agates.
Identifying Ellensburg Blue Agate: A Step-By-Step Guide
Rhyolite Outer Matrix: The Secret Sauce
You wouldn’t be the first to wonder what makes blue agate from Ellensburg so special, after all, normal blue agate can be found in a few other places too.
Well, according to studies carried out by Central Washington University, the secret ingredient that separates Ellensburg blue agate from the rest, is the surplus of rhyolite rife across the claims surrounding Ellensburg.
Rhyolite is the most silica-rich igneous rock in the world. It has a fine-grained or sometimes glassy texture and is composed primarily of sanidine, plagioclase, and, of course, quartz.
It can be gray in color, but up in Ellensburg, it’s much more likely to be a sandy or reddish brown color.
Typically, basalt plays host to agate, so this is an interesting divergence.
True Ellensburg blue agate is formed by geothermal liquid solidifying within rhyolite fractures over the course of roughly 50 million years, which has an interesting effect on the chemical composition of the final product.
The impact of rhyolite being the host rock is a highly elevated zirconium content in the blue agate, a super strong, silvery metal. No other form of agate will have this compositional element, making it the true signature of Ellensburg blue agate.
So, if your find has an outer shell of sandy or reddish-brown rock, there’s a good chance it’s rhyolite, meaning it’s possible that within is some genuine EBA, but let’s not get ahead of ourselves; there are more identification tests to come.
Goethite Inclusions
There should also be some goethite interspersed in the rhyolite matrix, between the rhyolite and the agate, and threaded into the agate itself as inclusions.
Goethite can be soot-black in its finely-grained form and jet-black in its glassy form, and is considered to be one of the most thermodynamically stable iron oxides on the planet.
Gemologists in and around the Ellensburg area consider goethite inclusions a prime factor in the classification of genuine Ellensburg blue agate, so if you can’t see any, it’s not looking good.
If you can, brilliant! Move on to the next step for further confirmation that you’ve got yourself a genuine article.
General Inclusions
Ellensburg blue agate won’t just feature goethite inclusions, but a number of more typical inclusions too. If you’re unaware, inclusions are caused by any material or substance that becomes trapped within the gem.
The trapped matter creates little fractures that look like small bubbles or threads, and they detract from the clarity of the stone.
True Ellensburg blue agate will not look pristine by any means. It should have a rather milky core due to all these inclusions.
Color Banding
As mentioned earlier, blue agate can be found in many other places around the world, such as Brazil, Tibet, and even a few European locations, but you’ll almost always be able to tell them apart from Ellensburg blue agate by the color banding.
Blue agate from elsewhere will of course have blue banding, but those blue bands will run alongside bands of other colors; you might see some red or white banding, for instance.
But quality EBA is composed of blue banding only. There are many different shades of blue in these rare gems, but these blues will not be accompanied by any other color.
Thermal Conductivity Test
If you’re looking for conclusive scientific evidence that your gem is an actual Ellensburg blue agate, you’ll need to pick up something like this Hong thermal conductivity gem tester, as it’s understood that EBA has lower than normal thermal conductivity.
Once you’ve got your tester machine, take a reading of a normal piece of agate, and then try your potential EBA. The normal agate should register at about 10.1, and the Ellensburg blue agate should register markedly lower than that.
The Light Test
A lesser known fact is that some blue agate specimens, especially those with a lighter blue coloring, will look faintly pink when held in front of a powerful light source.
Now, obviously, this test isn’t specific to Ellensburg blue agate, as pretty much any blue agate will show pink under a strong enough light, but if you just want confirmation that you have an agate to start, this is a good trick.
Gray Or Blue?
There are decidedly more gray agates strewn across the famous alluvial fan of Ellensburg than there are blue, and in certain lights, the gray can look a little blue, but don’t be fooled.
They’re almost certainly gray with a bit of a bluish tint reflecting back into the gem from the outer matrix.
My advice if you’ve found agate that looks on the cusp between gray and blue is to take a sample from the bulk of the rock and file away the outer matrix.
If the blue tinge was just the result of light bouncing off the shell, your now naked specimen will be unmistakably gray. If the blue remains, then there’s every chance you’ve got some authentic Ellensburg blue.
Final Thoughts
Don’t sweat it if your rock didn’t wind up being the real deal, as now you know how to identify Ellensburg blue agate, you can refine your hunting methods, head back out to your favorite spot, and start the search over with increased chances of finding the fabled gem.
If after all these tests you’re still not sure about your sample, I’d recommend consulting a gemologist. They should be able to do some chemical tests and provide you with the certainty you’re craving.