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 Post subject: Moonstone vs Labradorite
PostPosted: Thu Jul 31, 2008 11:22 am 
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Greetings!

I recently bought some silver and "moonstone" jewelry from Nepal. The stones are pretty, great color, but are very included and some have little golden specs. How can I make sure they are moonstone as opposed to some other kind of feldspar? Some of the pieces remind me of nice labradorite, for example,
One of them looks like this: Image (alt+p)

Can you please tell me what characteristics distinguish moonstone and any tips for testing?

Thanks a lot![/img]


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 Post subject: Moonstone
PostPosted: Thu Jul 31, 2008 6:50 pm 
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from Shuman -- Gemstones of the World

Moonstone -- Orthoclase Feldspar (Potassium)
RI 1.518-1.526

Labradorite -- Plagioclase Feldspar (Sodium and Calcium)
RI 1.559*1.570

Separation test is refractive index. Specific gravity also differs.

John

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PostPosted: Sun Oct 26, 2008 1:59 am 
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Question John,

These 2 tests. Wouldn't the stone have to be out of the setting to carry them out?
I feel it's high time I start to understand gemology for myself, not just working with the end product. So if people can bear with me popping up from time 2 time with my questions I will. If I don't ask, I won't know!
Doing a course is my aim but at this moment not possible.

Merryn
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PostPosted: Sun Oct 26, 2008 9:40 am 
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You might be able to get a RI measurement as a spot from a cabochon. If the stone is faceted, you should be able to use the table to get a RI. if the ring/jewelry will fit in the RI meter.

rI will work better with flat polished surface out of the setting.


specifit gravity -- the stone has to be out of the setting.


Unfortunately, identification should be done before the stone is set.

Best of luck.

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PostPosted: Sun Oct 26, 2008 10:00 am 
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Thanx John,

That's good to know from my side of things.
It's a start for me. Just found the project on the left which should be of help, maybe I won't look toooo silly for long. My problem is I keep getting sidetracked and chasing all the different links. :smt101

Merryn.


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PostPosted: Fri Dec 04, 2009 6:25 pm 
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labradorite, under magnification, should show a dusty brownish-gray background. This beeing said, some clear gemmy labradorite won't show this particularity.


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PostPosted: Mon Feb 08, 2010 2:28 pm 
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Location: Sri Lanka
There is good market value for Sri Lankan moonstone.
When dealers buy they ask Is it Sri Lankan or African(Mainly Madagascar) If it is mada they refuse to buy.

They said RI of Mada is higher side (plagioclase) Sri lankan is in orthoclase range.This true? If it is ,this only enough to differentiate
origin ? No orthoclase moonstone occur in africa?

I kindly need explanation from experts in forum.

Thanks


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PostPosted: Mon Feb 08, 2010 2:38 pm 
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can't you have varying amounts of potassium and calcium similar to garnets that could or would overlap?? feldpars are weird.... and what if you have elevated levels of potassium along with sodium and calcium what would you have then?..if i remember off the top of my head doesn't one type need a 60% postassium level to be considered a certain type or vice versa..not sure of percentages buyt if i remember correctly it's not that ortho has potassium but that it's comprised of(don't remember exactly) 60% postaasium..or something along those lines so technically without sophisticated testing could you be sure? one is not 58% postassium or ..you catch my drift..will need to look it up to make sure..

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PostPosted: Mon Feb 08, 2010 2:47 pm 
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okay i see..they have many different varities that can and will bleed over into each other..so the only thing that seperates ortho from plagio or any of the plagio seris is (K)..thats the only difference..so like i was saying above if i remember there must be a certain percentage of (k) to be orthoclase...right? since the checical makeup is identical to oligoclase excpet for the (k) then what defines how much (k) to be considered ortho as opposed to plagio(oligo)..labradorite has some other thingas thrown in which seperates it but just like garnets i am sure some bleeding ober happens often
Like i have said before feldspars can get complicated..similar to garnets..thats why i leave that up to Dr. Hanneman, Tim, and the others who are garnet knowledgeable..stupid feldspars..can't be easy can you...heck no..lets just throw a whole bunch of junk in there to confuse you gemmo's and novices..ha ha that will teach you :cry: 8)

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PostPosted: Mon Feb 08, 2010 5:37 pm 
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Hi.
Your stone looks like it may be the white semi-transparent to translucent white/colorless labradorite coming from India. This material is NOT technically moonstone.
Check this thread:
http://www.gemologyonline.com/Forum/php ... +moonstone

Spot RI can often be done on mounted stones.


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 Post subject: Re: Moonstone vs Labradorite
PostPosted: Wed Nov 23, 2011 2:05 am 
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Hi

was going through this thread and am trying to comprehend
where to draw the line between moonstone and colorless transparent Labradorite!

Holding a stone which is colorless with blue adularescence or blue flashes like in moonstones. Got a spot R.Is of 1.55 n 1.56 and SG of 2.70. Fl: lw bluish n sw - orangy .

Based on above doesn't it belong to plagioclase feldspar? But what
would be the variety then?? I'm confused at this point as the Appearance n FL looks like orthoclase feldspar-moonstone variety but RI & Sg looks labradorite variety !!

Has anyone encountered this in recent times ?? Perhaps these does belong to orthoclase feldspar category with higher RI & Sg due to perhaps different origin which these comes from possibly Africa?? I'm not sure but I only know moonstones from
Srilanka n India which has clear RI And SG of orhoclase feldspar.

Any thoughts??

Cheers!

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 Post subject: Re: Moonstone vs Labradorite
PostPosted: Wed Nov 23, 2011 2:11 am 
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Forgot to mention that the stone I have is not a milticolored rainbow flashes effect only blue flash seen and is transparent.

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