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
16 Comments
Cuzscience@lemmy.world · 5 pts · 234d
Old petrology pun: I may be gneiss, but don’t take me for granite.
YtA4QCam2A9j7EfTgHrH@infosec.pub · 4 pts · 234d
Hell Yeah. That is some nice gneiss
BarneyPiccolo@lemmy.today · 3 pts · 234d
Nice gneiss.
Kolanaki@pawb.social · 2 pts · 234d
Gneiss fuckin' rock. 😃
Icytrees@sh.itjust.works · 2 pts · 234d
The layers are so cool. I wonder if the top is a different material or just oxidized.
Masterkraft0r@discuss.tchncs.de · 4 pts · 234d
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.
Icytrees@sh.itjust.works · 3 pts · 234d
That makes sense and it's good to know. I'll have to knowledge up on my rock facts.
Thanks!
Masterkraft0r@discuss.tchncs.de · 2 pts · 233d
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
Icytrees@sh.itjust.works · 2 pts · 233d
Damn, you brought your A game to this rock community. Those pics are fantastic.
Masterkraft0r@discuss.tchncs.de · 2 pts · 233d
what can i say? i do like rocks. ¯\_(ツ)_/¯
SreudianFlip@sh.itjust.works · 3 pts · 233d
Yep. Quoting my geomorphologist family member here:
Masterkraft0r@discuss.tchncs.de · 2 pts · 233d
alright! sandstone then. it doesn't have limestone though. nothing on that rock reacts to acid
SreudianFlip@sh.itjust.works · 2 pts · 233d
Ah excellent! It's likely my family member is just tugging my leg to counter the tired but gneiss pun.
Masterkraft0r@discuss.tchncs.de · 2 pts · 233d
the more i think of it the more i doubt the sandstone again. i found this in a bigger region of high grade metamorphic rocks (mostly amphibolite, granulite). the specific place is a quarry where they quarry serpentinite as gravel. the rock unit is extremely busted up and crumbles basically on light touch into fist and smaller sized chunks. this rock, whatever it is, formed in cracks between the serpentinite. also for a straight forward sandstone this has a lot of mica in it and there are bands of nearly pure mica. i need to see if i can make take a picture with the microscope tomorrow.
SreudianFlip@sh.itjust.works · 2 pts · 233d
Well, I will be happy to relay the results to get the ubergeek response and report back. He loves his job.
Masterkraft0r@discuss.tchncs.de · 2 pts · 233d
great! thanks!