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NorthBen
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Joined: 29 Feb 2012
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NorthBen
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 Fri Apr 09, 2021 6:29 pm |
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These interesting formations were seen on an attempt of Moapa Peak, north of Las Vegas, in what looks like limestone. Some kind of concretion? Or?
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Mike Collins
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Brushbuffalo
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Location: there earlier, here now, somewhere later... Bellingham in between |
Good find, Mike. I concur. The only word I would modify is 'embedded', which possibly implies deposition of chert clasts as the limestone forms. Instead, the chert forms in situ ( 'in place') in limestone. Small but important difference.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Mike Collins
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Would saying the chert is an "inclusion" be appropriate? I have seen red jasper occurring in a similar presentation in limestone. When I saw the red jasper I was canoeing the Green River in Utah. I knew immediately than someone would have made arrowheads nearby. So I went to a shady locale under a rock overhand and sure enough there was a pile of chips about 1/2 meter tall the result of knapping likely thousands of arrowheads.
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Brushbuffalo
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| Mike Collins wrote: | | Would saying the chert is an "inclusion" be appropriate? |
Yes.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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TheWanderingIndian
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I found a few of these rocks on freedom peak near Navaho peak in the teanaway area. They were everywhere above 5000ft. The one side is kind of crystal like. But I’ve never really seen blue coloring in Rocks like this before. Like rocks I’ve found in the woods. Anyone have an idea what it is?
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Mike Collins
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Serpentine rock is usually green in color but can also come in blue shades. Looks like serpentine rock to me which is common in that locale.
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Brushbuffalo
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Before I get to 'geologizing' I'll just say that this is a really cool material....a bit mysterious appearing and downright attractive, and also not so common that we take it for 'granite' 
'Serpentine' is the name for a group of minerals formed by the metamorphic process of serpentinization into a rock serpentinite.
Basically serpentine forms when ultramafic rocks such as peridotite or dunite ( low- silica intrusive igneous rocks) are subjected to moderately increased pressure but low heat. Water is added the the original minerals and expansion in volume results in the slippery-feeling and shiny-looking surfaces that most of TheWanderingIndian's pictures show. This forms as the material differentially expands along surfaces almost like miniature faults rather than uniformly as in inflating a balloon.
We can find serpentine around margins of the Twin Sisters as well as near the Ingalls Peaks and elswhere in Teanaway country, near where you found your specimens.
Vegetation is often marked by unique species due to the mineral content of soil in ultramafic and serpentinized bedrock.
Mottled light to dark green is the usual color. I can't recall seeing blue samples before.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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rbuzby
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rbuzby
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Tue May 18, 2021 1:11 pm |
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I have a pic of a green rock taken near Lake Ingalls, always wondered what that was. It's Serpentine!
Since old questions are being answered, here's another. What caused this rock to look like this? I wish I had a closeup.
Lots of layers, two thick white layers, then, what happened? an earthquake maybe? Caused a crack right through the layers, with one side going down and the other up, relative to each other? Then, it somehow got transformed into microwave oven sized chunks, with grass growing up around them, and ended up near Pass No Pass, near Buck Creek Pass.
Thanks for sharing your knowledge.
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fourteen410
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Brushbuffalo, I've got one for you that I've been meaning to ask about for awhile. This is from the lakeshore of Dusty Lake near Quincy.
Why do rocks near desert water sources turn white? Is it agricultural runoff or is there something about the desert environment that does this?
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Malachai Constant
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There is a big face of Serpentine on the South Ridge route on Ingals Peak at first it links impossible slippery green wall but there is a crack up the middle class 3-4. Neat rock though it is also the parent rock for Asbestos with more metamorphosis.
"You do not laugh when you look at the mountains, or when you look at the sea." Lafcadio Hearn
"You do not laugh when you look at the mountains, or when you look at the sea." Lafcadio Hearn
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rbuzby
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rbuzby
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Tue May 18, 2021 1:44 pm |
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| fourteen410 wrote: | | from the lakeshore of Dusty Lake near Quincy. |
One of the lakes below the Dry Falls, below Grand Coulee, has white along the shore like that. I think it might be because the Army dumped chemicals in it many years ago.
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Brushbuffalo
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| fourteen410 wrote: | | Why do rocks near desert water sources turn white? Is it agricultural runoff or is there something about the desert environment that does this?
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A desert or even a semi-arid climate, such as the Dusty Lake area, has a net deficit in precitation vs. evaporation. Because dissolved ions will remain in the water when evaporation occurs, the ion content in water becomes higher than in more humid climates. When water continues to evaporate the ions ( largely alkalis such as sodium and calcium) will precipitate on solid surfaces above water level. This can happen even if the surface water body has an outlet if the dissilved ion content becomes high enough.
My hunch is that the source of the alkalis is natural chemical weathering but runoff from fertilizers may play a role in some cases.....or who knows, chemical pollution as rbuzby mentioned.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Brushbuffalo
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Location: there earlier, here now, somewhere later... Bellingham in between |
This is gneiss ('nice'), a high- grade metamorphic rock that is abundant.... even dominant.... in some areas of the North Cascades.
It is generally striking in appearance due to the separation of its minerals into bands of lighter and darker color.
The block in image center has a small fault, which is the result of stress causing the rock to not only break as in a crack ( joint ) but differentially slip ( be displaced) on opposite sides of the fault. Whether or not movement of this small fault was associated with a significant earthquake is hard to say, but in general faulting due to the strength of rock being exceeded is essentially what produces earthquakes, when energy radiates out from the source break.
This tiny fault serves as an avenue for mineral(s), quartz being most likely, to form the white vein along the fault.
Note the boulder at your left margin. That is a tectonic breccia, which is formed at depth, probably tens of miles down, where directed pressure is great enough to break rock but temperature is too low to start melting.
An assemblage of course angular boulders of varying sizes of one type such as the image shows is very often indicative of rockfall. A glacial moraine is another landform but they usually have multiple rock types unless the glacial is very small and localized. A quick view of the surrounding area is usually all it takes for an experienced observer to identify the landform.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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rbuzby
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rbuzby
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Tue May 18, 2021 3:38 pm |
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Thank You Brushbuffalo! That is fascinating information. Lots of violent stuff happening down there in the earth. This planet is so old. Just amazing.
Have you seen some of recent pics of the geology on Mars? I saw a shot of a conglomerate rock from Mars, like we might have here on earth. So cool. Good thing we have a magnetic field, or we might have ended up like Mars.
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