a publication of the International School of Gemology 26 September 2012

ISG: Rare Blue Feldspar (Okenoite)

This time it's for real!

I know what you are thinking: New and rare colored blue feldspar. Only one source that is difficult to reach. Unusual properties that are unlike almost anything out there. We have just danced this dance, have we not, with Tibet andesine? Well....

When ISG Community member Pete Brush came to me at the Tucson Gem Shows last year with a parcel of four blue feldspar crystals of about 1cm each in size, I was thinking to myself, "Damn, Pete, you really think I am going to fall for this again?" But after several go-rounds of testing and trying to apply what we learned about the fake Tibet andesine, I could find no "tell" that would say anything other than this material is genuine. And most recently, on another major gemology forum, it was discussed that advanced testing by L. Bruce Jones (GemScientist) showed the material to be genuine. (For those who don't know L. Bruce Jones, he is to the gemology profession what Usain Bolt is to the Olympic sprinter profession. The best collection of gemology toys and gadgets that make the rest of us drool, and he knows how to use them better than anyone in this industry)

The bottom line is that this is a very rare form of feldspar that is 90% albite with refractive index readings of 1.531 - 1.541. Specific gravity of 2.64 and pleochroism of light blue and colorless. With this information I decided to see what else we could find out using our grass roots level equipment here in the ISG office. Here are some interesting photographs that we hope will simply add to the outstanding work that L. Bruce Jones has done on this.
First, the pleochroism was beautiful with a light greenish blue color that emulates a natural untreated aquamarine of the finer qualities, although a bit more pale. As you can see in these images, the tendency toward the greenish colors will be affected by the angle of viewing in these three separate crystals. You can see the microphotograph at left and two more below. These were taken using our Meiji Techno microscope at 20x along with a London Dichroscope that can be obtained from the Gem-A.
I also found that, just like the Mexican and Oregon feldspar, this blue feldspar demonstrates the same reaction to long wave and short wave ultraviolet radiation. Below is a slide file of the crystals in ambient, long wave and short wave. The main difference is that this blue material reacts much stronger to the short wave than the other types of feldspars. The red color is far more pronounced in this material.

Dixie Magnetic Hydrosphere

Perhaps the most fun was comparing the magnetic reaction of the new blue feldspar with that of the Mexican and Oregon feldspar in our collection. As you can see in the slide show at left, the Oregon Sunstone demonstrates paramagnetism, meaning we can pull the specimen around our special Dixie Magnetic Hydrosphere magnetism demonstration tool. The black mark on my thumb is where I dropped a brick on my thumb. Pay no attention to that. The key factor is that these feldspars will be attracted by the magnet.

At right you see one of the blue feldspars in our same Dixie Magnetic Hydrosphere, but this time the magnet is being used to actually push the specimen across the water as it repels the magnet. An interesting difference in the two feldspar's reactions demonstrates just how amazing this previously disrespected gemstone can be.

I have no clue just how much or how little of this material Pete Brush has available, but he is the only guy I know that has it. This is very pretty material with a very soft blue color with slight green overtones that the images above don't do justice. If you want to obtain a very rare form of feldspar that offers a very unique color, this is the gemstone. You can find Pete at his website: Western Gem

We know Pete as "RuffysDad". If you have not met Ruffy....then its time to visit the site anyway. Its well worth the visit. Ask Pete about his Okenoite....and about Ruffy.

 

If you have problems viewing the images in this edition, please visit the ISG Student Forums to see the entire article on our website.

If you would like to study more about the importance of magnetism in gemology, we urge you to visit Kirk Feral's GemstoneMagnetism.com. Also read Dr. D. B. Hoover's work: "Magnetic Susceptibility for Gemstone Discrimination". We further acknowledge the work of Sylvia Gumpesberger, Magnetic Separation of Gemstones, and Richard D. Armstrong, RGA, of Armstrong Gemmology for their pioneering work and research in the field of magnetic gemology.

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