21 February 2023
Posted by Callan Bentley
Trying to dredge up some blogging inspiration, but honestly I’m feeling underrested and overworked these days, and not particularly enthusiastic about writing. But here are some cool rocks I’ve seen lately; maybe you’ll find them interesting…
Antietam Formation quartzite at Sherando Lake, Virginia:
I was struck by how sugary the texture was, and the interesting joint patterns resulting in kind of bulbous forms.
Graded bed of bioclastic debris, Martinsburg Formation, near Mountain Lake, Virginia:
Several students and I took a trip down to the geology department at Radford University recently, and they took us out to see some cool local rocks, including this excellent bioclastic turbidite in the late-Ordovician Martinsburg Formation. I love that even the fossil debris can sort it out by size when dumped in a submarine basin.
Granite dike in biotite granite, Ragged Mountain Reservoir, Charlottesville, Virginia:
Ragged Mountain Reservoir is a nice place to see Mesoproterozoic-aged Blue Ridge basement complex. Here, you can see cross-cutting relationships between an older biotite-rich granitoid and a younger, more felsic granite that forms a tabular dike cutting across it.
Triassic fanglomerate of the Scottsville Basin, north of Scottsville, Virginia:
A beautiful poorly-sorted conglomerate/breccia that likely was deposited in an alluvial fan complex on the edge of the Mesozoic rift basin called the Scottsville Basin, a gash in the Earth that opened up upon the breakup of Pangaea and the birth of the Atlantic Ocean basin.
Kyanite quartzite of Baker Mountain, Virginia:
It’s hard not to love this rock. What gorgeous kyanite porphyroblasts! Absolutely stunning.
Blue quartz, Ragged Mountain Reservoir, Virginia:
Back to Ragged Mountain again for this one. I saw this last week while on a circum-reservoir hike in search of odd ducks. It has an interesting brecciated texture that I don’t totally understand. Any ideas, readers?
You deserve a rest!
The amount of accumulated writing in this blog is dumbfounding, and everything in it is a real gift to an old amateur geologist down in Botetourt county.
And that goes double for the fantastic open geology text.
And all the YouTube content……
So kind of you to say so. 🙂
take a rest if need be, will be here when you come back, you rock.
Thanks, so nice of you to say so! 🙂
I hope you can find it in you to keep blogging, because these rocks are awesome! Could you please expound on the various ways quartzite is formed?
It’s funny, but this term “quartzite” means different things to different people. Some people use it as a synonym for “quartz sandstone” or “quartz arenite,” which is to say, it has the meaning of a sedimentary rock to them. I’m using it to mean a *meta*sedimentary rock, a rock which used to be a quartz sandstone, but then recrystallized under metamorphic conditions. So that’s the way *I* would say “quartzites” form, but other people are more specific or more inclusive in what they mean by quartzite, and thus ‘the various ways’ that those quartzites form.
Fanglomerate of Scottsville is highly reminiscent of Culpeper Basin’s Waterfall conglomerate. Baker Mt. kyanite is very cool.
I thought so too (re: fanglomerate). Come down here and see some of these rocks sometime, Troy!
I have been a fan of your site for a few years now and it is always a treat to see you pop
up in my inbox. Fanglomerate was a new term, pretty neat stuff out there.
Take a snow day!
I love the blue quartz!!