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Is this Bornite crystals?

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I dissolved a layer of Calcite from a stone I found, underneath was a matrix of Epidot crystals and these crystals which I suspect could be Bornite crystals.

alt text

asked Dec 7, 2014 by ArniSveinn (200 points)

4 Answers

0 votes

Definitely looks like a copper sulfide. Bornite is a copper sulfide but rarely forms in crystallized examples like that, except at a few notable occurrences. Though its more likely to be chalcopyrite, which is much more prevalent and forms commonly in crystals. It could be other sulfides as well, so best to do physical tests such as hardness and streak.

answered Dec 8, 2014 by hershel (51,320 points)
0 votes

Thank you very much Hershel! At first I thought this might be Chalcopyrite crystals, but something about the crystal structure didn't seem to fit. To me this looks like two cubes have grown together, but they are not completely cubic. From what I read Bornite sometimes (although rarely) forms nearly-cubical crystals. Pyrite is hardly an option here because of the irredescent colouring of the crystals.

Anyway, I appreciate your answer and will try to do a streak/hardness test on them.

answered Dec 8, 2014 by ArniSveinn (200 points)
0 votes

I did a streak test, either it is black or dark-grey. Hardness test is not so easy as the sulfides have similar hardness and I am not equiped to do very accurate hardness test. The colours are becoming more visible now, it's about 1 and 1/2 week since I dissolved Calcite from them with Hydrocloric acid. Not a very good picture I took now, more to show colouring of the crystals.alt text

answered Dec 9, 2014 by ArniSveinn (200 points)
0 votes

I see the strong iridescence caused by the reaction with the acid. I am only saying its more likely chalcopyrite because of the tendency for chalcopyrite to frequently form in crystals and being much more common than bornite. Though if the locality you found this in has been known to produce bornite crystals, than it is a greater possibility.

answered Dec 11, 2014 by hershel (51,320 points)