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can anyone ID this deposit? (mander.xyz)

submitted 11 months ago* (last edited 10 months ago) by [email protected] to c/[email protected]

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‐-----------------------‐-update 11-11‐----------------------

After more research and some lucky talks I believe this to be epidote from tailings out of the Wolverine Mine, a few miles from where I found these pieces.

‐-----------------------‐-original post------------------------

Was rock hounding on the southern shore of Lake Superior. Found these green crystal deposits that formed like geodes, specimens are small, the largest is about the size of a corn kernel. A local said it could be chlorasolite but I don't think it matches based on color and clarity. Any thoughts would be appreciated!

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[–] [email protected] 8 points 11 months ago* (last edited 11 months ago) (1 children)

I have no idea what that is, but it looks beautiful. You should have someone point an XRF gun at it to get a reading of what it’s made of. What if it’s some spicy compound of Cd, Ni or As.

You could narrow it down with webmineral or mindat, but you might still be left with hundreds of options.

[–] [email protected] 2 points 11 months ago* (last edited 11 months ago) (1 children)

I'll check out those resources, thank you! I thought arsenic as well as I know they used to make green dyes from it. Guess I'll skip the taste-test for now haha

[–] [email protected] 3 points 11 months ago (1 children)

People generally think rocks are pretty harmless, but they really shouldn’t.

Once you know the basics of geology or mineralogy you can look up the metal composition of most of the rocks you find in your environment. After that, there’s no turning back. You’ll never want to lick another random rock again, and you’ll be more cautions about breathing in rock dust.

[–] [email protected] 1 points 11 months ago (1 children)

This is horrifying and not surprising. I found these pieces on a beach, but noticed they were ubiquitous in almost all the crushed gravel I saw in the town (driveways, fill under roads etc). They seem to have been using copper tailings for all sorts of construction for a long time. I hope it isn't some nasty concoction, if it is those towns are a fema project waiting to happen.

[–] [email protected] 1 points 11 months ago

Better send some samples to your local friendly mineralogist. Usually the geological survey of your home country should be able to help. There’s also a good chance these rocks contain boring silicon oxide hydroxide whatever with a little it of calcium and sodium thrown in for color. It’s too early to tell without having them properly analyzed.

[–] [email protected] 4 points 11 months ago (1 children)

Go shoot an email to your local university geology dept. They might even want you to mail the rocks in.

[–] [email protected] 0 points 11 months ago

They'll be my next step if I can't figure it out online easily. Really appreciating the feedback from here though, got a few new resources for this sort of thing, feeling hopeful I'll get this I'D by sundown.

[–] [email protected] 3 points 11 months ago (1 children)

My gut says chrome diopside, or something in that solid solution. But more than a photo would be required.

[–] [email protected] 1 points 11 months ago (1 children)

Found it in gravel that likely came from copper tailings if that helps.

[–] [email protected] 2 points 11 months ago* (last edited 11 months ago)

Copper tailings, you say? It could be a sulfate precipitate of some kind. Probably a mixture of anything and everything, with lots of iron in it. If so, the crystals would be more or less water soluble. If so, you really need to skip the lick test.

Iron sulfate is usually nice and green, but contaminants tend to alter the color. Also, there are other green sulfate compounds, so narrowing it down without XRF can be tricky.

[–] [email protected] 2 points 11 months ago

These look like a bunch of epidote (+- quartz) amygdules in a basalt

[–] SatansInteriorDsgnr 1 points 10 months ago

This honestly just looks like regular old peridotite in some sort of basaltic groundmass. The crystals would be made of olivine which is very green and the surrounding groundmass I'm not sure, something mafic to ultrmafic though.