Please help identify these crystals!

[idahogoldhunter]

These were pulled out of a decomposing rock sticking out of a hillside.

 

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[mamabear]

First off, name of state where you found piece would be helpful. Personally it looks like tourmaline to me. nice find

 

[Jim in Idaho]

Maybe black tourmaline? How hard is it?
Jim

 

[Jim in Idaho]

First off, name of state where you found piece would be helpful. Personally it looks like tourmaline to me. nice find

Mama, ya beat me to it...LOL
Jim

 

[idahogoldhunter]

It was found in Big Sky, Mt. Its hard enough that I can't scratch it with a steel knife.

It does sound like tourmaline! It is mostly in hexagonal formations with pretty parallel cleavage. The crystals range from 1-10 mm in length and are as wide as 5mm. They are scattered around in all different directions.

 

[DDancer]

Yep black tourmalines. Nice little species with good shape. Its normal to see tourmaline crystals in all sorts of orientations due to how the host rock is formed. Might get lucky and find some larger specimens with a bit of digging.

 

[mamabear]

Yes I would dig for more. Who knows what you might find. I am jealous, by the way.

 

[idahogoldhunter]

Really? I guess Ill go back down the road and break it up some more. I'll take some pics on what's beneath the surface.

 

[Eu_citzen]

I'd like to get a better picture of a cross section, down the length of the crystal. (the second pic)

I think it might be Pyroxene or amphibole. Tourmaline is also possible, but the cleavage of tourmaline is so poor, it usually isn't even noticeable to most.
Amphibole and pyroxene have a better cleavage. I'd also go back and look for more!

 

[idahogoldhunter]

 

[Eu_citzen]

Go and find someone locally that can help ID this stuff. The university, if they have a geology section or even a local rock club.
These are tricky to ID from a picture, if my hunch is correct, the pictures seem to reinforce that. (but then, that's just my opinion)

Parallel to what is the cleavage?

 

[mamabear]

EU, just for my curious mind, why do you say black Tourmaline cleavage is poor? I had a small piece & it was a similar break as in pic. I looked up "Pyroxene or amphibole" & I could not find either here in the states. Can you point me in the right direction for information on these 2 minerals? I am always anxious to learn of specimens unknown to me. Thanks, Mamabear.

I'd like to get a better picture of a cross section, down the length of the crystal. (the second pic)

I think it might be Pyroxene or amphibole. Tourmaline is also possible, but the cleavage of tourmaline is so poor, it usually isn't even noticeable to most.
Amphibole and pyroxene have a better cleavage. I'd also go back and look for more!

 

[Eu_citzen]

"Cleavage basics 101"

#1 The more "clean" the splitt - the better the cleavage. If it splits in one flat plane - its a perfect cleavage. Like Topaz.

#2 Don't confuse cleavage with fracture. Cleavage are splits among weaknesses in the crystal structure, fractures don't. Calcite is a good example of cleavage.

Tourmalines cleavage isn't very good in terms of how well it splits. It does usually not cleave into large flat spots. If it did - it'd be a lot more troublesome to cut.
If you can compare a cleaved topaz and tourmaline you'll know what I mean.

Pyroxene is a group name. Diopside, Augite and several others are all pyroxene family members.
Most can't be separated without more sophisticated tests, so we use the group name.

Amphibole is also a group name. Tremolite and Aktinolite are members, I think there are more.

 

[DDancer]

With the picture of the end breaks and tip termination it still looks like tourmaline. True, tourmaline does not cleave cleanly due to its crystalline structure, however considering just the base facts of location and the pictures cleavage is kinda secondary to identification.

The other groups of minerals described tend to grow in clusters. Tourmalines tend to resist clustering though twining is common. Coloration is also important however there are variations that resemble tourmalines in those other groups and many have a more rounded structure. This is just my thoughts coupled with my experience. Not a bad thought though

Pyroxene pictures : https://www.google.com/search?q=pyr...yDfPksATh9oCQBg&ved=0CD8QsAQ&biw=1366&bih=673

 

[Eu_citzen]

The problem I have is the crystals look monoclinic to me, there are also no striations so typical of tourmaline. Of course it could just be that exception to the rule.
Still, its the crystal structure that is my strongest source of doubt.

 

[DDancer]

In smaller crystals like the ones shown tourmalines often have very clean lines and monolithic appearance. I've found examples like the one shown in decomposed granites. The shape and terminations help to determine what they are. I've used orthorhombic charts in the past to figure out what I'm looking at and am seeing something I've identified in the past.
Hehh If I'm wrong I don't mind either. Its crystal, its shiny and I like it

 

[idahogoldhunter]

That makes total sense as the crystal shown is the larest sample obtained. Also they were discovered in decomposing granite. They are all octagon and some are growing out of each other at odd angles. When crushed they form a white powder.

 

[Eu_citzen]

To settle this I'd recommend having someone local look at it again.