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Bornite is my best guess... any other thoughts?

Posted by Matt Courville  
Matt Courville March 13, 2018 02:41AM
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?

Edited 1 time(s). Last edit at 03/13/2018 02:42AM by Matt Courville.
Alfredo Petrov March 13, 2018 03:02AM
Chalcopyrite, I think.
Wayne Corwin March 13, 2018 03:07AM
Chalcopyrite is my guess too.
Volkmar Stingl March 13, 2018 05:23AM
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?

Edited 1 time(s). Last edit at 03/13/2018 05:24AM by Volkmar Stingl.
Wayne Corwin March 13, 2018 05:46AM

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.
Alfredo Petrov March 13, 2018 05:50AM
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.
Reiner Mielke March 13, 2018 12:59PM
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.

Edited 2 time(s). Last edit at 03/13/2018 01:09PM by Reiner Mielke.
Matt Courville March 13, 2018 03:42PM
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?

Edited 1 time(s). Last edit at 03/13/2018 03:43PM by Matt Courville.
Reiner Mielke March 13, 2018 04:40PM
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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