Hi Guys and Girls during the happy hour last night a gentleman came up to me and showed me some black stones which he said were Black Sapphires and they came from the lava fields of FNQ. These pieces that he showed me looked extremely dark (the lighting was not too good in the hall) with the broken side being quite glossy like crystal. The stones are all around 8 to 10 mm all round measurement. He also had another dozen stones around twice as big that looked like Apache Tears, when held to the light you could see through. The smaller stones when held to a light could not be seen through. The gentleman said that he had brought a parcel of the Black Sapphires which contained about 100 stones, and asked if I could cut him a couple in return for a few of them. He gave me 8 of small stones and when I got home had a look with a small LED torch and found that some that the light came through. The stones had the appearance of being Obisidium like Apache Tears, not all of them let light through. My experience with the Lava plains Sapphires are that they show a dark blue if the light could come through. As not having any other material to compare them with I am at a bit of a loss as to whether they are Black Sapphires as claimed or a material similar to Apache Tears. What would be the best way to cut them. I know that they are not going to have a lot if internal light reflection.
One quite simple way to find out if it is an Obsidian or Sapphire would be to do a hardness test . Obsidian 5 to 5.5 Mohs. Therefore, if a Quartz can scratch it, it would certainly not be a Sapphire, in which case an RI for Glass would be correct. Although a very dark stone cannot be cut for brilliance anyway.
Reg Do a SG test
and the best way to cut them no matter what they are. is to make cabochons
If they are too dark to see through, you could cut a 95% table with small 45 degree bevel on the back then a high crown like a half sphere, maybe checkerboard design, and rely on light reflected from the surface for sparkle.
Thank you for your input, they are not sapphire as Quartz and Zircon will scratch them.
May cut one as per Gordon,s suggestion. Thanks Guys
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