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I think you have tourmaline crystals in feldspar and a little bit of mica.

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That. ^^^

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to me it looks like a chunk of pegmatite, with alkali feldspar, quartz and biotite mica.

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Posted (edited)
On 3/10/2019 at 10:46 AM, fuss said:

to me it looks like a chunk of pegmatite, with alkali feldspar, quartz and biotite mica.

I agree that it has basal cleavage like biotite. I still have a lot to learn about rock and gem structure. Is the cleavage of tourmaline on a vertical plane also considered basal cleavage since it breaks off in "strips or sheets"?

When I read the definition of biotite, it mentioned it as being more of a brownish colored mineral but this picture looks black to me.

biotite_image1.png

Edited by 23XLive

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On 3/10/2019 at 11:46 AM, fuss said:

to me it looks like a chunk of pegmatite, with alkali feldspar, quartz and biotite mica.

This ^^^

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There is no tourmaline visible in the original photo  - the dark mineral is Biotite mica. Tourmaline has no perfect cleavage like mica - like the minerals in the original photo. Biotite is dark colored and may be nearly black. If you cleaved off a thin flake of it, it likely would be dark brown. 

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