The scattered white rocks of the Sierra

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CAMERONM
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The scattered white rocks of the Sierra

Post by CAMERONM » Sat Feb 15, 2020 3:19 pm

I have wondered for years about seemingly random white rocks I find in the Sierra. They can be semitransparent, and sometimes also have a brownish tinge on some facets. They almost never appear as a solid area or even a solid vein; the pictures I show are quite unusual and exceptional for the quantity shown. I recall seeing more of them on the top of Mount Longley and Lone Pine Peaks, and perhaps more in the south, but they seem to appear pretty much around and on top of all the top peaks. Any clue what they are and why they are so dispersed?
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Wandering Daisy
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Re: The scattered white rocks of the Sierra

Post by Wandering Daisy » Sat Feb 15, 2020 4:07 pm

As you can see in your second photo, the "white rocks" are more weather resistant than the rock they are initially in, so over time the parent rock holding them in gives away and the more resistant rocks fall out, later to be moved downslope by gravity, rain or snow melt. Quartz and feldspars can be whitish or pinkish. These rocks (inclusions) form when the magma cools, different crystals forming at different stages in the cooling. Slow cooling tends to make larger "white rocks". All this happens underground before the Sierra were uplifted. It has been a while since I studied such things, so someone like Giantbrookie who is a professional can chime in and perhaps I am a bit off on this.

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Re: The scattered white rocks of the Sierra

Post by bobby49 » Sat Feb 15, 2020 7:40 pm

If you go way back in time (hundreds of millions of years), the western coast of North America was about where the California-Nevada border is now. Slowly, little by little, the Pacific Plate came ramming into the North American plate. With that, the carbonate material which had been ocean bottom sediment got added to North America about where we call California. While most sediment is initially laid down horizontally and then maybe compressed there, lots of this newer stuff got uplifted and compressed more, and this made vertical striping along what we now call the Sierra Nevada Range. As this got compressed more, what used to be limestone was becoming white marble. Then the tops of the Sierra Nevada got eroded. This left some exposures of white marble in high places where you would not normally expect to find them. This also led to some of the most high-altitude white marble caves.

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Re: The scattered white rocks of the Sierra

Post by The Other Tom » Sun Feb 16, 2020 5:14 am

Interesting discussion. I'm not a geologist, but the rock you're holding looks like quartz (primarily silicon dioxide) to me. I think WD is right about the feldspar, too. Yeah, we need Giantbrookie on this one.

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Re: The scattered white rocks of the Sierra

Post by bobby49 » Sun Feb 16, 2020 10:38 am

Yes, the above rock photo looks like Milky Quartz.

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Re: The scattered white rocks of the Sierra

Post by mort » Sun Feb 16, 2020 12:40 pm

While you see them as small and scattered, try the cirque that (old) Army Pass is atop. There are huge chunks of the stuff, some bus sized laying amongst the other talus. Shining like giant ice cubes. I'm looking for a picture in my 36 mm archives. This one, from July 2019, is on the west approach to Army Pass about 11,000 ft. It is buried in the moraine, about 1 foot comes out above the ground.
quartz.jpg
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Re: The scattered white rocks of the Sierra

Post by Harlen » Sun Feb 16, 2020 6:23 pm

mort writes:
While you see them as small and scattered, try the cirque that (old) Army Pass is atop. There are huge chunks of the stuff, some bus sized laying amongst the other talus.
I ran into huge quartz rocks on the ridge between Foerster Pass and Lyell Fork of the Upper Merced Basin:

Bench Canyon 457.JPG
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Last edited by Harlen on Tue Feb 18, 2020 11:24 am, edited 2 times in total.

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Re: The scattered white rocks of the Sierra

Post by CAMERONM » Mon Feb 17, 2020 10:19 am

@halen @mort, I don't think that I have seen veins that large. I find it curious that these little white rocks can show up quite singly.

New Army is south. Does it seem to others that these rocks tend to be more present in the south?

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Re: The scattered white rocks of the Sierra

Post by mort » Mon Feb 17, 2020 2:06 pm

New Army is south. Does it seem to others that these rocks tend to be more present in the south?
Hi Cameron,
Harlen's great picture from the heart of Yosemite indicates that quartz veins can bee seen in all the Sierra and nearby mountains. In California the richest gold lodes are in quartz veins associated with serpentine. A large gold nugget (about 10 lbs) found in Randsburg, called the Mojave nugget, shows that there must be a gold vein near Mojave, south of the Sierra, The biggest nugget found in California was from Sierra Buttes, north west of Tahoe, in the northern end of the Sierra. I think you can find small quartz inclusions almost anywhere in the Sierra, and a few well known big veins. Near Saddlebag Lake there were several mines, gold and silver and other metals mostly. The biggest was the May Lundy mine at about 11,000 ft. on Mt. Scowden. It produced about 5 tons of gold from 1880 to 1900. I mention it because the gold was mined from a huge quartz vein that ran right through the mountain. The geology of the Saddlebag lake area is a fascinating melange. There is definitely serpentine and quartz, and just about everything else.
-mort

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Re: The scattered white rocks of the Sierra

Post by oldranger » Mon Feb 17, 2020 11:14 pm

When I started reviewing this thread I immediately thought of the outcropping Harlen posted below Forester in Yosemite.
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I also recall the huge shelf of quartz shown below while wandering up thru the lakes in East Pinnacle Creek.
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