edit1: Some more photos of this selfsame rock through a micro scope (somewhere between 10x and 45x, didn’t write it down)

and another feature I discovered: the rock has a slickenside which i can’t really show on a photo. basically one of the sides is beat up into sand and polished. the whole rock unit was pretty beat up, so i’m not super suprised but it’s cool

edit2: ok i tried to capture the slickenside

    • Masterkraft0r@discuss.tchncs.deOPEnglish
      2·
      6 hours ago

      Disclaimer: So, I am very interested in this topic but i am no petrologist or anything. So take everything I say with heaps of salt. But:

      From what I understand though it’s different materials. Gneiss is highly metamorphosed, meaning subjected to high heat and/or high pressures. So the source rock (often granite) is squeezed and stretched and the discrete crystals stretch into this layers. It’s also pretty easy to see under any optical magnification, that there are different types of crystals and minerals in the different bands. At least to the untrained eye it looks like it.

        • Masterkraft0r@discuss.tchncs.deOPEnglish
          1·
          3 hours ago

          i posted a few microscope pictures up top. what i neglected to mention is that the stretched crystals recrystalize, so single crystals won’t lock stretched under the microscope. but you can (maybe) see the white crystals, which is quartz, then some brownish stuff, which is either impure quartz or mica crystals, and some black platey stuff, which may be biotite mica

          but please: see disclaimer in above post. i could be talking out of my ass