D4RR3N
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Test for genuine Turquoise?
Can anyone think of a very simple chemical test to confirm real turquoise from fake dyed stones, howlite etc. Turquoise is aluminum phosphate with
small amounts of copper so I was thinking a phosphate test of come kind would do the trick
any ideas?
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elementcollector1
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Copper test would probably be more suitable.
What about the standard mineral tests? Scratch plate, Mohs hardness, etc.?
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D4RR3N
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Testing hardness requires equipment, I just want some test that will identify if copper or phosphate is present.
I just want to crush a small sample into powder and drip a solution on it and get a positive or negative result.
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HgDinis25
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Actually, testing hardness could only require a piece of glass, a nail, a finger nail, and some knowledge.
Anyway, heat it up with concentrated Sulfuric Acid in a test tube. If it's Copper Phosphate it should form an equilibrium, thus coloring the solution
blue. Watch out for phosphric acid fumes.
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D4RR3N
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Fake turquoise is dyed blue so it may turn the solution blue anyway?
Perhaps a phosphate test would be more accurate since turquoise is the only gem stone to contain it whilst copper may be common to many.
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elementcollector1
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No, concentrated sulfuric acid would likely destroy the dye.
Copper is not very common in gemstones - come to think of it, I can't think of any other major gems containing copper... Unless as trace impurity.
Azurite maybe? But it's a very different shade than turquoise...
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D4RR3N
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Malachite contains copper in a high degree, formula for Turquoise is actually CuAl6(PO4)4(OH)8ยท4H2O it is not copper phosphate as someone above
stated.
so basically I heat some crushed turquoise with conc sulphuric acid and if it turns blue its genuine turquoise?
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elementcollector1
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Pretty much, yeah. Dyed howlite would just dissolve to a clear solution (destruction of dye and dissolution of the Ca/B/Si oxyhydroxide).
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unionised
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If I'm reading things correctly, unhardened mild steel will scratch howlite but not turquoise.
If I was looking for something to dye howlite, I might use a copper based dye like monastral blue or even a solution of copper sulphate.
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zed
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A lot of fakes are actually mineral stuff, stuck together with resin. Touch the tip of a red hot pin to the backside of your purported turquoise.
If it melts, it's bogus.
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