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Identity HelpMystery crystal #3

25th Sep 2019 01:05 UTCDerek Lowe

I found this crystal recently at Robillard Mountain, near Craigmont, Ontario.  It has several sharp corners and flat edges, a shiny lustre, and is quite hard (sorry, I don't know how to estimate the actual hardness yet).  Any thoughts on what this might be?

25th Sep 2019 01:05 UTCDerek Lowe

Pic #2

25th Sep 2019 01:05 UTCDerek Lowe

Pic #3

25th Sep 2019 01:06 UTCDerek Lowe

Pic #4

25th Sep 2019 01:34 UTCAndrew Debnam

Derek, find a piece of Quartz and see if it scratches it. If it does then given the area it is from you have Corundum. 

25th Sep 2019 01:49 UTCBob Harman

ANDREW, I think you are meaning to say CORUNDUM.

Maybe microcrystalline quartz....quartzite??  CHEERS....BOB

25th Sep 2019 01:57 UTCDerek Lowe

I have a piece of quartz and it couldn't scratch the crystal, so that means the mystery crystal is pretty hard :)  What about the shape of the crystal itself - does it look like it might be corundum?

25th Sep 2019 02:00 UTCAndrew Debnam

Too funny  Bob, yes Corundum.  I have the conundrums……..

Derek, you should check the learning centre tab at the top right of the mindat page.  Click on learn. Don Peck has created some good articles including how to determine hardness. 

25th Sep 2019 02:30 UTCAndrew Debnam

perhaps, tough to tell from your photo what crystal shape might. The link below provides some good guidelines which will help the Mindat community give some information on your finds

25th Sep 2019 02:31 UTCDerek Lowe

Thanks for the tip.  I actually used to know how to do a lot of this about 35 years ago, but that knowledge has long since leaked out of my brain...

25th Sep 2019 02:41 UTCAndrew Debnam

Derek, I have experienced some leakage as well...…..we all do

25th Sep 2019 03:20 UTCKeith Compton Manager


It would also help to ensure that the subject specimen is placed on a flat surface and then photographed. Holding it in your hand creates movement and results in an out of focus photo.

Doesn't look like a crystal of anything to me from the photos.

25th Sep 2019 04:10 UTCTama Higuchi

Like Keith said, this doesn't appear to me like any sort of crystal; I don't see any definable structure/form.

25th Sep 2019 12:01 UTCDerek Lowe

What about the defined smooth edges?  Is that considering more cleavage than crystal?

25th Sep 2019 17:23 UTCA. Mathauser

To me it's some kind of feldspar (anorthite/labradorite...?). Hardness 6-6,5 (less than quartz). Perhaps more clear pictures would help...

25th Sep 2019 19:03 UTCTama Higuchi

I would second the feldspar guess.  Reminds me of the rough, non-iridescent side of my labradorite piece.

25th Sep 2019 20:31 UTCAndrew Debnam

The geology of the area needs to be considered. Generally speaking the Craigmont area is a syenite pegmatite. So Quartz depleted. Bronze coloured Corundum is commonly found in a buff coloured syenite. When cleaved the planes may appear in photos to be quite iridescent.  In addition the outer surfaces of the Corundum alter to Mica.  If Derek can check the hardness to see it over 7 then I would still favour Corundum. I have attached a quick photo (-not great I know)of a bronze Corundum shard from the locality I collected. It does make very nice cabachons as well. Over to you Derek to see if you get a good handle on the hardness

25th Sep 2019 20:49 UTCDerek Lowe

Thanks for the info.  I tried scratching this sample with a piece of quartz, as suggested, and it did not scratch this sample, so it is definitely pretty hard.  I have also attempted to take better pics - not sure if they are any better or not but they are in natural light and as well-focused (and resting on the ground) as I can get...

25th Sep 2019 20:49 UTCDerek Lowe

Pic #6

25th Sep 2019 20:49 UTCDerek Lowe

Pic #7

25th Sep 2019 20:49 UTCDerek Lowe

Pic #8

25th Sep 2019 22:45 UTCMatt Courville

I'm confident that you have a section or roughly formed corundum crystal.  The 2nd photo top section is the best givaway fom my point of view.  The scratch test added to this - if using your mystery piece to scratch quartz appears to make a mark, then it is almost certainly corundum.  There are some subtle varieties around this general region with the corundum found with hints of red, blue, and black coloration.  Keep your eyes peeled for anything odd;)


25th Sep 2019 23:21 UTCLloyd Van Duzen

I agree with Matt.  Your material is similar to what can be found at the Burgess Mine.  From the buff syenite as Andrew mentioned. You have pieces of corundum crystals. 

26th Sep 2019 01:17 UTCDerek Lowe

Thanks guys, for the info.  I do hope that it is corundum, of course, but in any case I really like the sample due to its many sharp edges and interesting lustre.  I am so new to this (started this past August) that any cool sample I find is a great addition to my collection.

17th Oct 2019 00:48 UTCDerek Lowe

Well, I went to the ROM clinic and the verdict is: Corundum :)

17th Oct 2019 13:26 UTCAndrew Debnam

Thanks for the update Derek Good you could drop into the clinic

23rd Oct 2019 21:04 UTCDerek Lowe

Yes, it was very educational.  I also had a fossil that I found 35 years ago and it turns out it is a Cephalopod from 450 Million years old - twice as old as the dinosaurs!

I plan to go mineral collecting a few more times before the snow flies this winter, so hopefully I will have some more samples to take to the December ROM clinic.

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