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Identity HelpUnknown Black Mineral?

23rd Oct 2016 00:48 UTCJasmin Ward

08106430016030940064587.jpg
Hi, I was wondering if anyone has an idea of what this is. I received this from someone & the location is unknown (sorry!). I think I've seen it somewhere before but I'm having a hard time finding it anywhere. I searched through many pictures of black minerals on here & on Google, & noticed that it has some similarities to Geothite, ferro pargasite, and schorl tourmaline. It also has another mineral on a part of it. It scratches easily with the point of a knife & has a metallic luster when it catches light w/ a light gray/blue streak. I also have a picture of a brown rock that I don't expect anyone to try to identify, but if you can then go for it. Thanks!

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23rd Oct 2016 01:09 UTCDennis McCoy

The first one may be stibnite

23rd Oct 2016 01:31 UTCAlfredo Petrov Manager

The first thing you need to do, Jasmin, is rub a corner of it over a piece of unglazed porcelain (like a broken cup or something) so you can tell us what colour streak you see (the colour of the mineral's powder). If the powder is black, you may have a metallic mineral like stibnite or a sulphosalt; blue could indicate vivianite; pale grey, white, or greenish white could be a silicate like kyanite or amphibole; yellow-brown might be goethite.... Then there will be other tests to do, but I think checking the streak color would be the easiest and most useful to start with in this case.

23rd Oct 2016 03:24 UTCJasmin Ward

Thanks for the feedback & advice. It has a light gray/blue streak.

23rd Oct 2016 07:23 UTCVolkmar Stingl

Dennis McCoy Wrote:

-------------------------------------------------------

> The first one may be stibnite


I don't think so.

Maybe possibly actinolite or any other type from the hornblende-group (I think I can see rhombic transverse sections).

23rd Oct 2016 07:44 UTCUwe Ludwig

Hornblende rsp. Actinolite was also my first idea.


Rgds.

Uwe Ludwig

23rd Oct 2016 09:07 UTCGreg Dainty

Brazilian kyanite?

23rd Oct 2016 10:12 UTCMark Heintzelman 🌟 Expert

07565550016030940079543.jpg
Agree with Greg, looks like it may be a Jequitinhonha valley Kyanite (Minas Gerais, Brazil).


23rd Oct 2016 11:46 UTCAndrea Oppicelli

The first photo I suppose : hedenbergite

23rd Oct 2016 21:31 UTCJasmin Ward

Thanks for all of the great feedback! Black Kyanite looks like an exact match.

24th Oct 2016 00:54 UTCReiner Mielke Expert

If it is Kyanite you could not have scratched it easily with a knife.

24th Oct 2016 01:05 UTCDoug Daniels

Kyanite could be easily scratched by a knife in the long direction, but not across the short direction.

24th Oct 2016 01:51 UTCReiner Mielke Expert

Kyanite has a hardness of 5.5 in the long direction that is near the upper hardness limit of a steel knife. see: http://www.mindat.org/forum.php?read,7,356076,357007#msg-357007 so it would not be easy to scratch. However there could be something soft between the crystal blades. I would recommend trying to scratch across the crystals to verify that it is not easily scratched. Another possibility is that it is coated with laquer or similiar to enhance the color that would give a false hardness.

24th Oct 2016 04:04 UTCAlfredo Petrov Manager

Doug seems to be right - We might have to modify what Mindat gives as the hardness of kyanite. I just tried scratching a blue brazilian one with a knife point and it was really easy to scratch parallel to the long axis. Webmineral gives the hardness difference as 4 - 7, which seems closer to the truth.
 
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