What kind of rock is this?

[smeagol]

Hi. Can anyone tell me what kind of rocks these are?

Thanks!!

[charlieb]

Kinda looks like tourmaline? Please tell us more about it: where you found them; their MOHS hardness; color streak. Thanks. Chuck.

[smeagol]

Thanks for your quick response. I didn't find the rocks; I bought them at a tropical fish store. They were in a big box with other rocks, but these were the only three of this kind. I have never seen anything like them in a fish store before. I don't know what MOHS harness is; how do I measure that? They have a sandy/gritty texture. The colors are mostly black and gray, with a little bit of orange/rust color here and there. The lines are very thin and straight, almost like a very fine-grained wood. And they are very "sparkly" overall like glitter. (Please forgive my non-technical description; I know almost nothing about rocks/geology.)

[charlieb]

Hardness: Try scratching it with a pocket knife blade. If the blade scratches it, try apiece of glass. Let me know. Chuck

[smeagol]

Yes, you can make very fine scratches in it with a pocket knife. It even seems kind of brittle, like you might be able to flake bits of it off by tapping it with a hammer. It has a very coarse/sandy feel. As I handle it, it leaves grit on my hands, and there's grit accumulating in the cardboard box.

Thanks for your help!

[broseph82]

Def looks like black schorl tourmaline smeagol