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Identity HelpBornite is my best guess... any other thoughts?

13th Mar 2018 02:41 UTCMatt Courville

Bornite is my best guess... any other thoughts on this one, which sits on calcite with some cubic pyrites and a base of heavy iron based rock

It comes from the well known Marmoraton Iron Mine in Ontario. I have been told by one knowledgeable collector that they had also collected here what they believed was bornite - identified by it's 'peacock' purple color.

This is the best I can produce as far as photography goes. Suspected material in centre areas. Could it be anything else in this type of environment?

13th Mar 2018 03:02 UTCAlfredo Petrov Manager

Chalcopyrite, I think.

13th Mar 2018 03:07 UTCWayne Corwin

Chalcopyrite is my guess too.

13th Mar 2018 05:23 UTCVolkmar Stingl

I see cubes and striated faces - pyrite. Also the pale golden colour points to pyrite (or arsenopyrite). Therefore my vote for prite. What is the streak colour?

13th Mar 2018 05:46 UTCWayne Corwin

Volkmar

Yes, there is pyrite cubes all over, but there is (in the centers of the photos) a golden mass with no crystal shape to speak of, that has taken on the typical purple. blue and red tarnish colors of chalcopyrite.

Working off those photos and only based on that, with no other info, I still say chalcopyrite.

13th Mar 2018 05:50 UTCAlfredo Petrov Manager

Volkmar, If you look at Matt's original question, he already knows that pyrite crystals are present. His question was about the iridescent purple-tarnished grains. I agree with Wayne that those are probably chalcopyrite.

13th Mar 2018 12:59 UTCReiner Mielke Expert

Could just be tarnished pyrite which is common there. Have never seen bornite from there. Check the hardness with a needle. Pyrite harder than a needle chalco & bornite softer. Untarnished bornite is brown, chalco golden.

13th Mar 2018 15:42 UTCMatt Courville

Thanks for the help

Reiner - I have used super iron out on pyrite in the past and noticed that it seems to loose all of it's tarnish. Do you suppose this would allow the bornite/chalcopyrite/pyrite to be identified better once the color is gone; leaving either a brown or golden finish?

13th Mar 2018 16:40 UTCReiner Mielke Expert

The needle test is the easiest assuming you have a microscope. Pyrite at times is difficult to distinguish from pyrite based on color but the hardness difference is obvious.

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