slightly yellow cut orthoclase 190 carats

[kunky45]

Hey, I found this straw colored clear orthoclase stone in an old mica prospect here in Georgia then I had it faceted. The original weight of the piece was over 400 carats. The faceted stone is 190 carats.
I am wondering how common this material is. The stone is exceptionally clear.

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[arappaho]

Can't help you with your question, allthough I think it's a good one.
Figuring out anything about the Feldspars is a constant struggle
for me.
But thanks for posting a picture of that beauty!
Nice find and a job very well done!
Joe

[rockshine]

Don't know either. but in a quick google and ebay said it was somewhat rare for facet grade, except in madagascar. As always, color has a lot to do with the value, and the Madagascar stones are listed from cheap to several hundred dollars. Beautiful stone

[kunky45]

I have spent a great deal of time over the last year searching the internet to accumulate info about the stone my wife found.
We were working in an old mica mine(prospect) that never produced much mica. Also, it seems to be a pegmatite that produces only malformed crystals. I have never found a good quartz crystal at this mine. One day my wife was scratching around and found what we thought was something that was unusually clear. It turned out to be about 450 carats.

We have used two different systems to get the specific gravity. Every time it comes up about 6.0.
Orthoclase seemed to be the closest mineral. It does not have any reflectance like andularia.

Very small stones are dirt cheap on ebay so I just forgot about it. About 1 year later I saw a much large stone like this listed for pretty big bucks.

I determined that this stone was so clear that I mailed it off to Thailand and had it cut and faceted. It is a very nice piece and the guy that cut it said it was very clean. Now it weighs 190 carats.
One of the guys that responded to my post said there is very little info available for orthoclase, and I would agree.
One can find orthoclase listed in the rock books, but they always seem to be talking about the white, chalky phase which is one of the most common minerals on earth.
I don't see much of the clear phase turning up in the USA. I wanted to find out if others in the USA have found this type of stone.

From Charley Brooks - March 14, 2012 at 08:09:20
Email: brookscharles[ ]bellsouth.net

[Barrett]

All you have done for ID is specific gravity? You have not taken the R.I. or had it tested in any other way?

[kunky45]

No, I don't have big bucks to have it analyzed. It only cost me $65.00 to have it cut and faceted.
With that sp. gravity, it's got to be in the feldspar family. We have found other pieces of this--all in the tabular crystal form.

[Barrett]

If the specific gravity is 6 then how did you come to orthoclase, which is a 2.55–2.63 SG? Thats a pretty wide margin to assume. Some glass is closer to that SG than orthoclase.
Red flags are popping up with the stone being..."the guy that cut it said it was very clean"..and.."The stone is exceptionally clear"
You rarely just "stumble" upon something like this that why it's best to err on the side of caution before assuming you have a giant flawless orthoclase gemstone..
A report from AGL in New York will cost less than what you paid for cutting it and if you truly believe it's a big clean piece of ortholclase then another $55 for confirmation and peace of mind means nothing.
I have a guy in Maryland that would probably test it on the cheap for you He is a GG, and a competant one at that, with all the proper tools to test it. Thats a very nice stone so getting some documentation in hand would be of utmost importance

[kunky45]

Sorry. that was a typo. Correct sp. gravity is 2.60.