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Is this a mica crystal?

Posted by John Montgomery  
John Montgomery April 28, 2012 10:55AM

Thanks for any help

Edited 2 time(s). Last edit at 04/28/2012 03:29PM by John Montgomery.
Vik Vanrusselt April 28, 2012 11:23AM
It sure does look like mica to me. Which species is hard to say from a photo...

John Montgomery April 28, 2012 12:49PM
Here are some better pics... can click on pic to make it a bit larger.

The first pic shows the clean face.

The second pic shows the opposite face that is covered with some black substance, but you can still see the shiny face coming through: can this be cleaned? I have already soaked it in Super Iron Out.

2.3 cm x 1.5cm x 1.8cm ( I haven't done a scratch test because I don't want to wreck it in case it is mica)


Edited 4 time(s). Last edit at 04/28/2012 03:28PM by John Montgomery.
open | download - DSC05608.JPG (785.3 KB)
open | download - DSC05610.JPG (747.3 KB)
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Spencer Ivan Mather April 28, 2012 01:43PM
It deffinately looks like mica to me, but it is impossible to tell what mica from a photo.

Donald Slater April 28, 2012 04:03PM
I don't think it is mica. I would expect to see some layering. As they say it is very hard to tell details from a photo. It almost look like some corundum I have seen. The easiest way to tell the difference is a scratch test. You could do a very small scratch test on a corner on the face with out too much damage. Another way would test specific gravity. This is a little more involved. Corundum has a much higher density so you might be able to get a feel for it. Does it feel heavy when you bounce it in your hand?
John Montgomery April 28, 2012 04:09PM
Thank you Vik, Spencer and Donald.
Donald, no, it doesn't seem all that heavy, but I'm not very experienced.
I have recently done a specific gravity test using Reiner's easy method, so I'll do that and report back.
Maggie Wilson April 28, 2012 04:12PM
Knowing John's collecting environs, I'd say it's a mica crystal.
John Montgomery April 28, 2012 04:28PM
Hi Maggie!
I just did Reiner's specific gravity test and got 1.9 which is a lot closer to SG of mica than corundum... so I guess I can assume mica Maggie...thanks
I'm kind of amazed because every mica piece I've seen in the field has been broken!...and this is quite perfectly shaped.
Maggie, would you know how to clean that black stuff off the mica, safely?

Edited 2 time(s). Last edit at 04/28/2012 04:36PM by John Montgomery.
Maggie Wilson April 28, 2012 07:29PM
Safely? the short answer is "no." My advice is to leave the piece as it is, warts and all. At the most, swish it around in a container of water. However, if you are willing to risk losing it in order to test the limits of cleaning mica, then you might give it a gentle wash under the tap, or VERY gentle squirts with a spray bottle.

One caveat - I'm not the chief cook and rock washer in this household - what I suggest above are my guesses - others with more experience, please chime in!
Neil Mathieson April 28, 2012 08:11PM
Are you sure it's not Staurolite.

Photo 1 and 3 does look like a mica, but photo 2 does not.

Photo 2 made me think of staurolite.

Just a thought.
Stephanie Martin April 28, 2012 08:34PM
My vote is for mica group, however the SG is still off, perhaps it is being replaced by something? Did you do the test once or try more than once to see if the result is repeated?

Based on your SG result this does not fit staurolite, that is more closely comparable to the range of corundum.

I agree with Maggie on the cleaning, it may do more harm than good if too aggressive.

stephanie :-)
John Montgomery April 28, 2012 08:55PM
Yikes Stephanie!...thanks again. I re-did Reiner's test...twice and discovered I got the volume of the specimen wrong the first time (5 instead of 7) thus making the Specific Gravity
Looking at the Mindat page for mica, that puts it pretty close ( not using distilled water)
And thanks Maggie and Stephanie re: cleaning... I will leave it fact the more I look at it, the more interesting it becomes as is!
Stephanie Martin April 28, 2012 09:31PM
John, glad that second try worked well, and that does pretty much confirm mica group as you said.

stephanie :-)
John Montgomery April 28, 2012 09:41PM
...and a third re:do just for good measure: SG 2.6 :):)-D
Andrew Johns April 29, 2012 05:15AM
Could it be be a Muscovite after Corundum? I have a piece from the Burgess Mine that is partially pseudomorphed to Muscovite. Where was it found John??

Edited 3 time(s). Last edit at 04/29/2012 05:23AM by Andrew Johns.
John Montgomery April 29, 2012 11:50AM
Hi Andrew,
I collected it in the Gatineau area near Ottawa...I'll check out your photo page... but it s quite light (SG 2.6)

Maybe we will cross paths collecting in the Bancroft area ...I am planning on checking out the Burgess Mine soon... If you have any collecting tips from that mine I'd appreciate them ( I read Michael A.s article)
thanks for your input
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