I am new to this but I need to be able to identify genuine black spinel as opposed to black onyx. I realise spinel is harder but is there a way to tell them apart easily? Is there some simple test equipment I could buy?
I should mention that I am trying to make the identification of stones that are already set in silver jewellery. I live in THailand which apparently is one of the few sources of black spinel having a mine in Kanchanaburi but even local traders there refer to black spinel as being black onyx - hence my confusion.
The faceted black spinel which I saw a lot of in Thailand and which was all referred to as "black onyx," had a noticeable higher luster and sharper faceted edges - they both are listed as having vitreous luster in texts, but side by side, I see a luster difference. If you buy some specimen stones for comparison I think you will see the difference - especially with a loupe and a good light.... look at the fracture surfaces (spinel is chonchoidal and vitreous) and see if light behind the stone shows any banding near the thin edges. A refractometer reading would be your best proof, though not always possible of course - the black spinel will have a higher RI than other spinel - 1.740 up to 1.777, much higher than chalcedony (black onyx).
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