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 Post subject: moonstone or labradorite???
PostPosted: Wed Oct 02, 2019 9:23 pm 
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Hello everyone! I’m new here and I am madly in love with gems and jewelry, but for some reason, I’ve always had trouble telling the difference between orthoclase moonstone and (labradorite) Rainbow moonstone. Recently I bought a necklace with flashy moonstones and I was wondering which It might be. I want to say it’s orthoclase, but I’m just not sure?? ANY help will be much appreciated!
Thank you! ♥️

I’ve attempted to downsize the photos, so forgive me if I wasn’t successful. Please! :oops:

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 Post subject: Re: moonstone or labradorite???
PostPosted: Wed Oct 02, 2019 10:27 pm 
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This appearance is typical of labradorite rather than orthoclase moonstone. Typically orthoclase has a more diffuse sheen, and though it ranges to blue it doesn't typically come out this blue.

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 Post subject: Re: moonstone or labradorite???
PostPosted: Wed Oct 02, 2019 11:29 pm 
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Some years ago I asked Dr. Rossman if translucent colorless or white labradorite can be called "moonstone".
He pointed out that "moonstone" is not a mineralogical term. It is a tradename.
Image
Mineralogically, the stone above is labradorite from India.
It is also a moonstone. :wink:

To seperate labradorite from orthoclase:

Optic Character:
Labradorite: Biaxial POSITIVE
Orthoclase: Biaxial NEGATIVE

Refractive Index:
Labradorite: 1.559-1.568 (± .005)
Orthoclase: 1.518-1.526 (± .010)

Specific Gravity:
Labradorite: 2.70 (± .05)
Orthoclase: 2.58 (± .03)


PS. Your stones are labradorite.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Wed Oct 02, 2019 11:44 pm 
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Stephen Challener wrote:
Typically orthoclase has a more diffuse sheen


Ah, I see. Well that makes sense actually, because I have a piece of orthoclase moonstone that isn’t blue and it appears the way you describe. I feel kinda silly now. Thanks for the information!


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 Post subject: Re: moonstone or labradorite???
PostPosted: Wed Oct 02, 2019 11:48 pm 
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Barbra Voltaire, FGG wrote:
Some years ago I asked Dr. Rossman if translucent colorless or white labradorite can be called "moonstone".
He pointed out that "moonstone" is not a mineralogical term. It is a tradename.
PS. Your stones are labradorite.


Thanks for the information! :D This has made me realize most of the blue moonstones I’ve bought in the past 18 years are likely mostly Labradorite.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Thu Oct 03, 2019 8:17 am 
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Very high end orthoclase moonstone begins to resemble rainbow moonstone more. Preumably that comes down to the thickness of the exsolved compositional layers. Apparently labradorite has some sort of thin layer diffraction going on, while orthoclase usually has thicker layers that produce maye scattering of light.

I have an old gem dictionary from 1950 or so that already mentions rainbow moonstone, so I figure that fight came and went well before I was born. The really poor material can be kind of ugly, but the toppest end rainbow moonstone, with a water clear base and brilliant play of color, is one of the nicest gems you could hope to see. Also tends to be priced accordingly, it was something over 500/ct at AGTA when I saw any.

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 Post subject: Re: moonstone or labradorite???
PostPosted: Thu Oct 03, 2019 10:54 am 
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Stephen Challener wrote:
Very high end orthoclase moonstone begins to resemble rainbow moonstone more. Preumably that comes down to the thickness of the exsolved compositional layers. Apparently labradorite has some sort of thin layer diffraction going on, while orthoclase usually has thicker layers that produce maye scattering of light.
Stephen Challener wrote:
I have an old gem dictionary from 1950 or so that already mentions rainbow moonstone, so I figure that fight came and went well before I was born. The really poor material can be kind of ugly, but the toppest end rainbow moonstone, with a water clear base and brilliant play of color, is one of the nicest gems you could hope to see. Also tends to be priced accordingly, it was something over 500/ct at AGTA when I saw any.


Yeah it makes perfect sense to me the difference now that it’s been pointed out to me. :oops: I see a lot of beautiful higher end orthoclase in antique jewelry. The cabochon makes it easier for me to tell the difference I think.
-
Oh wow. I didn’t realize rainbow moonstone was around that long... Yeah, and I agree with you on that. I have some pretty pieces of rainbow moonstone, but for the most part they are cloudy and with not much color. The gems in this necklace aren’t of the highest quality, but I like the piece anyhow. :D


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 Post subject: Re: moonstone or labradorite???
PostPosted: Thu Oct 03, 2019 12:36 pm 
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Moonstones were very popular in the Victorian period. All the intact moonstone pieces I have seen from that period have been orthoclase feldspar. The character of orthoclase moonstone is fairly diagnostic. It looks a little sleepy.

When I see a period piece with labradorite, I suspect that the original stone has been replaced.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Thu Oct 03, 2019 12:45 pm 
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Do you tend to see stars and cat's eyes in these pieces as well? Or just straight sheen?

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 Post subject: Re: moonstone or labradorite???
PostPosted: Thu Oct 03, 2019 12:50 pm 
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Barbra Voltaire, FGG wrote:
Moonstones were very popular in the Victorian period. All the intact moonstone pieces I have seen from that period have been orthoclase feldspar. The character of orthoclase moonstone is fairly diagnostic. It looks a little sleepy.

When I see a period piece with labradorite, I suspect that the original stone has been replaced.


Oh wow, yes. I ended up not buying an antique ring in England once with a moonstone exactly like those pieces and I kick myself now. It is quite sleepy looking. There’s something magical about the sheen to me. I guess now the only pieces I have that are orthoclase are one or two loose gems I’ve had since I was very young. I have some earrings that seem older and could be, but now I’m not sure about these either.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Thu Oct 03, 2019 1:14 pm 
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Stephen Challener wrote:
Do you tend to see stars and cat's eyes in these pieces as well? Or just straight sheen?


Straight sheen...adularescence. But I certainly have not seen every moonstone piece made at the turn of the last century.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Sun Oct 06, 2019 12:02 pm 
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Jolielaide, your earrings don’t look that old, they look like that kind of silver jewelry mass made somewhere in Asia, and they might very well be made of onyx and moonstones (but not the best, with blue sheen, quality).
All I say is just what they look like, and from a picture only, no certainty.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Sun Oct 06, 2019 12:04 pm 
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I'd go with India. Contemporary.


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 Post subject: Re: moonstone or labradorite???
PostPosted: Mon Oct 07, 2019 6:52 pm 
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I've been playing with both moonstone and rainbow moonstone for quite a while, for no particular purpose. If ever there was two types of gem mineral with overlapping characteristics, it is these two. I can endorse pretty much everything Barbra and Stephen say here.

As described above, when one knows what to look for, translucent (orthoclase) moonstone is relatively easy to distinguish from translucent (labradorite) rainbow moonstone.

It becomes more tricky to distinguish between water clear types of each material showing only one blue color. At some point, without a raman spectrometer, you may not be able to tell the difference. I've included a couple pictures to show just how similar the different materials can look.

The first photo is three stone on a black surface, oriented to show as much blue in each as possible. Quoting Sesame Street, "one of these things is not like the others."
Attachment:
moonstone black.jpg
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The second photo shows the same stones arranged on typed letters "o" on white paper, oriented to show just hints of blue color. This demonstrates the transparency of the stones.
Attachment:
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Of course both material offer more than just the blue color effects. Orthoclase moonstone can demonstrate chatoyancy (cat's eye)... and it comes in translucent forms of different body colors (brown, orange, yellow, green). And labradorite itself is most familiar in opaque black body color, like spectrolite with all kinds of fancy color combinations. For some reason, I've acquired samples of all these things.


Last edited by Brian on Mon Oct 07, 2019 8:56 pm, edited 1 time in total.

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 Post subject: Re: moonstone or labradorite???
PostPosted: Mon Oct 07, 2019 8:45 pm 
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Those are great photos!
Not just chatoyancy in orthoclase either, but four and eight ray stars (which seem to be an expression of the adularescence) and six-ray (from hematite inclusions, like a black star sapphire).
Feldspars can be super addictive.

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