Well, schist!

Back to basics, a real rock.

The photo is about 4 cm wide.

Dark gray crystalline areas are, indeed, quartz. Whiter areas are not, but seem to be feldspar, or an altered growth of ex-feldspars. Brownish patches are essentially intergrown amphiboles. That's about all there is in this rock.

It's horrendously deformed, the white elongate bleb in the upper center essentially is a "boudin" of its former self.