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Identity HelpUnknown matrix from Huangang mining area, China

27th Mar 2013 12:03 UTCPhilip Mostmans Expert

Hi all,

I was hoping anyone might be able to help me with this one...

Attached is a close-up (cut out) of a larger foto of a Fluorite on matrix from the Huanggang mining area.

Minerals present on the specimen I have identified are Fluorite, Calcite and Arsenopyrite. This remains a mistery however.

The view in the photo is about 3-4cm wide. As you can see it is a black mineral, feels coarse to the thouch (no smooth faces). The mineral appears brittle and course, but can't be scratched with my fingernail.

The "crystals" are about 1cm long and show dense layering or growth stages. The mineral is strongly iridicent under a light source (direct or indirect), with a preference to the Bluish/purple.

Ideas anyone?

Thanks in advance.

Philip

27th Mar 2013 13:04 UTCUwe Kolitsch Manager

What's the colour of a fresh fracture surface? (If you can't find one, create one.)

27th Mar 2013 13:18 UTCPhilip Mostmans Expert

The colour of a fresh fracture appears to be a silvery grey, with a hint of brown.

27th Mar 2013 14:51 UTCUwe Kolitsch Manager

Then it could be arsenopyrite or löllingite.

30th Mar 2013 10:52 UTCPhilip Mostmans Expert

Hi Uwe,

Thank you for the reply.

What makes the Arsenopyrite/Lollingite look so different from the ones in the other pictures?

The coarse/iridescent look seems not very typical for either mineral.

Best wishes,

Philip

30th Mar 2013 14:32 UTCReiner Mielke Expert

Can you scratch it fairly easily with a nail, not the blue coating but what is under that? Loellingite and arsenopyrite cannot be scratched with a nail but bornite and chaclopyrite can and are also commonly tarnished blue like your sample. Have never seen Loellingite or arsenopyrite tarnished like that which makes me think they are not either of those.

31st Mar 2013 14:24 UTCPhilip Mostmans Expert

Hi Reiner,

Thank you for your insights. Think you might be on to something here.

I doubt it to be Chalcopyrite, but Bornite/Chalcocite could definately be an option. I attached a photo of the complete specimen and to the left of the Bluish stuff, I definately notice an increase in brown color. This color seem to originate from a mineral coating other crystals (perhaps Chalcocite?).

Thanks for the help!

Best wishes,

Philip

31st Mar 2013 15:29 UTCReiner Mielke Expert

If the fresh material has a distinct brown tint ( as opposed to gold) then it would be bornite, chalcocite is dark silver blue-grey very different from bornite and chalcopyrite. Fresh chalcopyrite would be a gold color but can tarnish blue like your sample.

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