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kpinwalla2
Social climber
WA
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May 18, 2010 - 11:04pm PT
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In case you're interested, I wrote a book about the evolution of granite landforms in the City of Rocks. It's called "Etched in Stone" - available from the Idaho Geological Survey. What you guys are calling "solution pockets" are actually called panholes, armchair hollows, and tafoni. In Germany they're called "opferkessel" and "gnammas" in Australia. They don't necessarily need a zone of hydrothermal alteration to initiate. Solution is only one of many processes that contribute to their formation. Rowl Twidale of Australia is "the man" when it comes to granite weathering - he literally wrote the book - "Granite Landforms".
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adam d
climber
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May 18, 2010 - 11:28pm PT
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Minerals... thanks for the lesson!
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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May 18, 2010 - 11:54pm PT
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That's a strange feature. Doesn't look natural. Hard to imagine a natural process that would bore a tunnel through granite like that. I agree with Minerals that it might possibly be a hydrothermally-altered, xenolith that was more vulnerable to normal weathering processes and was eroded out of the granite.
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Fritz
Trad climber
Hagerman, ID
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May 19, 2010 - 12:00am PT
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Kpinwalla2: Thank you for info on your City of Rocks publication: "Etched in Stone"
I will buy it, so I can learn more, and understand less about: Idaho geology.
However: a truly open and enlightened mind, might well ask if those holes in Yosemite Granite may relate to current ST posts on the artifact on the far side of the moon.
Minerals??? Are you covering up other theories?
Think of the headlines: "Alien Wormholes in Yosemite!!"
Then again: those holes may have grown giant------ and now eroded crystals.
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Mighty Hiker
climber
Vancouver, B.C.
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May 19, 2010 - 12:06am PT
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Maybe it was made by wonky space aliens, who thought they were making crop circles. :-)
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pyro
Big Wall climber
Calabasas
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May 19, 2010 - 12:09am PT
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Hey minerals geology about Yosemite is way cool.
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Shack
Big Wall climber
Reno NV
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May 19, 2010 - 01:24am PT
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Bryan is a great source of information that I'll never understand.
Excerpt from last weekend:
Me:"Hey Bryan, what's this?" (me holding up a some interesting looking rock I found)
Bryan:"A rock"
Me:"Oh yeah, right, hehe..."
a couple minutes later:
Me:"Hey Bryan, I think I found a quartz crystal!"
Bryan:"Nope, that's calcite."
Me:"Damn,....It looks cool though"
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nutjob
Trad climber
Berkeley, CA
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May 19, 2010 - 03:03am PT
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OK, what about these things on top of Lower Brother?
Off-thread question, but the pics were nearby. Where is Phantom Pinnacle in this photo?
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kpinwalla2
Social climber
WA
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May 19, 2010 - 09:47am PT
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First photo is a pod of pegmatite with what looks like big crystals of k-feldspar
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pc
climber
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May 19, 2010 - 10:31am PT
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Thanks very much for the posts and info Minerals!
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cragnshag
Social climber
san joser
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May 19, 2010 - 10:44am PT
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good stuff, maynard!
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Minerals
Social climber
The Deli
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May 20, 2010 - 08:39pm PT
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Jeff and others, glad to be of help and thanks for all of your replies! I always like talking about rocks, even if it is about this surface stuff that I don’t know so well... ;)
Yeah, that north wall on Wawona looks like it needs some more bolts, Jeff! :) Maybe have to pay you a visit some time.
Thanks, Fritz! But I didn’t do any research really, and am just a wannabe igneous petrologist – I’ve never studied weathering in any detail and am certainly no geomorphologist. Just gave it my best shot off the top of my head. Those are some cool photos that you posted, especially the second one! Don’t tell the sport climbers about that place… I tend to doubt that the weathering in your first photo is due to hydrothermal alteration but that is something that would be best explained by a local geologist, like Kpinwalla2, who understands that stuff better than I do. I’ve only been to the City once, and that was a looong time ago, before I studied rocks. Neat place.
“Geology: The more I learn, the less I know.”
Yes, most certainly! I remember saying to a professor about 10 years ago… “The more I know, the more I don’t know.” Isn’t that the truth! But it’s good in that it makes us continue to question and to ask why… otherwise things would get kinda boring.
Kpinwalla2, thanks for posting up! Yeah, my use of the term “solution pocket” is pretty much climber slang and shouldn’t be regarded as proper geologic terminology. Thanks for catching that. My geomorph terminology could use some help, big time. So, those are “panholes” on the top of the boulder in Nutjob’s second and third photos? Aquarium Rock too?
http://en.wikipedia.org/wiki/Panhole
So, this is your book?
http://www.idahogeology.org/Products/reverselook.asp?switch=title&value=Etched_in_Stone:_The_Geology_of_City_of_Rocks_National_Reserve_and_Castle_Rocks_State_Park,_Idaho
And this is the book that you speak of, by Twidale?
http://www.amazon.com/Granite-Landforms-C-R-Twidale/dp/0444421165/ref=sr_1_1?ie=UTF8&s=books&qid=1274385955&sr=1-1
Whew…! 300 bones, if you can find one…
How about this one?
http://www.amazon.com/Landforms-Geology-Granite-Terrains-Charles/dp/0415364353/ref=sr_1_2?ie=UTF8&s=books&qid=1274385955&sr=1-2#noop
Or this one?
http://www.amazon.com/Granite-Landscapes-World-Geomorphological/dp/0199273685/ref=sr_1_4?ie=UTF8&s=books&qid=1274385955&sr=1-4#noop
Tradster, with regard to the tube on Wawona Dome, I wasn’t thinking of an altered xenolith, just altered granite. Of the holes that I have seen in Yosemite, none of them appeared to be related to xenoliths or any other inclusions in the rock, but all have evidence of alteration of the granodiorite. Cool sculpted staircase! J-Tree?
Pyro, is that malachite?
http://en.wikipedia.org/wiki/Malachite
Image: http://en.wikipedia.org/wiki/File:Azurite_with_malachite_and_others.jpg
Shack, don’t forget gypsum!
Nutjob, as Kpinwalla2 said, that’s pegmatite, a very coarse-grained, granitic rock type. Aplite is roughly the fine-grained equivalent of pegmatite, although pegmatite may contain additional accessory minerals, as well as some “weird” minerals. In your photo, it looks like the pegmatite is part of a dike, as you can see more pegmatite in the bottom of the photo. The large crystals of pink potassium feldspar (K-feldspar or K-spar) look like they make up the center of the dike. The white feldspar is plagioclase and the rust-colored stains are due to the weathering of iron-bearing minerals, such as hematite or magnetite. Pegmatite can be really cool looking, especially when tourmaline and other neat minerals are present. Pegmatite can also be mafic/gabbroic in composition and contain large crystals of mafic minerals (dark in color).
http://en.wikipedia.org/wiki/Pegmatite
http://www.pegmatology.com/basic_info.htm
http://geology.about.com/od/rocks/ig/igrockindex/rocpicpegmatite.htm
http://www.gemandmineral.com/peg.html
Here are a few more photos of weathered granite in Nevada…
Evening light. I sent this photo to a professor who looked at the photo and described the rock as “weathered rat shit”… I guess I have to agree, but it’s still nice to look at and fun to explore. We are spoiled by the clean, glaciated exposures in the Sierra.
Neat patterns
A series of panholes (correct, Kpinwalla2? Or are these armchair hollows?)
Potholes in drainage
Panholes, fine-grained mafic enclave with negative weathering relief, and xenolith of schist with positive weathering relief – schist wins
Kpinwalla2, what do you think about the features in these photos? Anything to add?
Here’s a video of a trip down a really cool drainage in the same area as the above photos. The quality is pretty crappy – my 4-megapixel free-bee camera isn’t so great for video and it doesn’t adjust exposure for changes in brightness/darkness (video is too dark at times…). It also won’t film for very long. It stopped and I had to start it up again, but the exposure is much different (brighter). Anyways, it’s not so great, but gives you an idea of how cool this maze of slots is. Gotta go get a new point-n-shoot…
Desert granite slots:
http://www.youtube.com/watch?v=wEFIpKQaAok
Any of you J-Tree locals seen stuff like this down there? How ‘bout in the City of Rocks?
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pyro
Big Wall climber
Calabasas
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May 21, 2010 - 01:26am PT
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minerals it's just a small sample of Uranium from Africa. I wonder if you guys have ever run accross that stuff in the sierras? (just curious)
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R.B.
Trad climber
Cascadia
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May 21, 2010 - 01:40am PT
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I think a lot of the "weird" formations we find in climbing are mostly related to the processes of wind and water weathering ... together with the inherit mineralogical variability of intrusive granitic batholiths.
I think those holes were probably formed from water action.
Just an opinion.
RB
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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May 21, 2010 - 01:47am PT
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Yes the photo I posted is JTree, Split Rock area. Here's another photo showing an ice-filled pocket at the top of the Blob taken on Jan 1, 2008.
Pyro: your mineral looks like Sklodowskite. Mg(UO2)2Si2O7 - 6H2O
Is the sample from the Shinkolobwe mine in the Congo?
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Robb
Social climber
The other "Magic City on the Plains"
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May 21, 2010 - 11:50am PT
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Any of you guys/gals found the galium deposits in the valley?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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May 21, 2010 - 01:05pm PT
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No please tell us where the Gallium deposits are.
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