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Brushbuffalo
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PostFri Nov 24, 2017 7:57 am 
GC99 wrote:
Fluorite
Good identification, GC99, and I'm buying it. Fluorite is not a particularly common mineral in these parts but superficially resembles quartz. The greenish color should have tipped me off. I was hasty in hypothesizing it was aqua aura quartz ( highly improbable) or prasiolite (rare, and so far as I know, not found in the North Cascades). This is an example where examining from pictures can lead to strange guesses. In the hand, fluorite ( hardness of 4) will easily be scratched with a knife, but quartz (h=7) will not scratch. GC99 and others : Please help with identifying the oddities that are bound to be coming in. We appreciate expertise.

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Brushbuffalo
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PostFri Nov 24, 2017 9:23 am 
moonspots wrote:
rock from capitol forest
rock from capitol forest
It's about 1 1/2" square for a size reference. Notice the small cavities with a slight blue tint (bottom center of rock image)? They were quite a bit brighter (but still a pale blue) when I first cracked it open maybe 6-7 years ago. I found only a very few of these in a creekbed in the hills maybe 15-20 miles west of Olympia.
I'm calling the rock a basalt porphyry ( dark groundmass with macroscopic but still small crystals...the tiny, barely visible light specks, not the obvious large whitish objects ). This basalt is from the Crescent basalt formation, which is widespread on the Olympic Peninsula. The cavities are vesicles ( very common in basalt). I can't tell from the pictures for certain, but the white minerals could be quartz, calcite, or a zeolite. Let's say they are quartz. Quartz does not occur as a primary mineral in basalt but after a flow cools and sits there for umpteen millenia, silica-saturated fluid can penetrate the basalt, find its way into the vesicles, and crystallize. The largest partially filled vesicle in your picture shows particularly well-formed ( euhedral) crystals. These form because they are not competing for space with each other within the vesicle as growth occurs. Filled or partially filled vesicles make this an amygdaloidal basalt ( there's a good term to mention...casually as possible....at your Christmas party). I'm less certain about the bluish tint, however. It seems to be more on the basalt surface and may be due to microscopic ferromagnesian minerals such as pyroxene. The illumination might be ptoducing an effect, too. Note the difference between the "bluish" left face and the dark gray upper flat face.

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RichP
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PostFri Nov 24, 2017 9:27 am 
Here's my contribution. Found in the Chopaka Mtn area.
These rocks tell a story.
These rocks tell a story.

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Brushbuffalo
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PostFri Nov 24, 2017 9:34 am 
RichP, yours appears to be a spectacular example of sedimentary breccia. The prominent banded clast in center is gneiss, derived from bedrock gneiss somewhere in the vicinity when the sediments forming the breccia were deposited. A very poorly sorted breccia comprised of very angular particles indicates rapid deposition and a short transport distance, such as a landslide. Edit: Once again, jumping to a premature conclusion. I see on my larger monitor that there is an angular block of gneiss that is merely resting on top of the brownish rock. I originally thought this and the other blocks were part of the larger rock, hence my comments about rapid deposition forming a very poorly-sorted breccia. I am not familiar with the specific geology of the Chopaka area. The brown rock may be tuff breccia, a volcanic material made of subangular and angular macroscopic particles held within a finer-grained matrix of ash. The larger fragments are largely crystalline and phaneritic (coarse grained), indicating a plutonic source before being fragmented and lithified as a volcaniclastic rock. Phew! Lots of terminology there. And I may be all wet! One thing's for sure...fascinating rock!

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daffish
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PostFri Nov 24, 2017 11:55 am 
Crystal Formations on brown rock
Crystal Formations on brown rock
Crystal Formations #1
Crystal Formations #1
Crystal Formation #2
Crystal Formation #2
crystals were in the talus and boulders in the immediate foreground
crystals were in the talus and boulders in the immediate foreground
Small example
Small example
small rock example
small rock example
I have always been curious as to what this formation is. From the first picture, I thought it was a type of fossil, but I am not so sure now. These were found in the basin west of Silvertip Peak in the Monte Cristo area. They appeared mostly on the edges of the boulders and talus in one small area with the rays of the formations about 1" - 2.5" long. On the smaller rock which I brought home, the rays are quite short and not as pronounced.

"Be moderate in everything, including moderation" Horace Porter
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Brushbuffalo
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PostFri Nov 24, 2017 2:14 pm 
daffish wrote:
Crystal Formations on brown rock
Crystal Formations on brown rock
I believe that this is a remnant of a vein that filled a fracture in the brown rock. The rock broke along the fracture, being a plane of weakness, and some of the vein mineral remained on this piece that you photographed. Sorry, but without having the sample in hand to check things such as hardness and angle between cleavage planes, etc., I won't venture a guess as to the specific mineral identity of your other pictures. Actually I will, but it's just a guess.There may be minerals in the heavily mineralized Monte Cristo area that I might not be familiar with. However, the long prismatic crystals in the prominent whitish mineral suggest it may be a member of the amphibole family. The fanlike habit of the crystals is interesting.

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moonspots
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PostFri Nov 24, 2017 2:27 pm 
Brushbuffalo wrote:
I'm less certain about the bluish tint, however. It seems to be more on the basalt surface and may be due to microscopic ferromagnesian minerals such as pyroxene.
The little pockets of "bluish tint" are not on the surface until the small shperical voids were broken open, but the blue was a brighter, (yet pale) color when the rock was newly cracked open. I wish I knew enough about rocks and minerals to have an idea as to what they might be. Maybe at Christmas I can get me son to take me back to where I found this and perhaps find another. Thank you (and all others) for offering opinions.

"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
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Brushbuffalo
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PostMon Nov 27, 2017 12:29 pm 
Doppelganger wrote:
Analcime was my first guess on this one as well
Analcime https://en.m.wikipedia.org/wiki/Analcime is generally considered to be a member of the zeolite family. It is a strong candidate for a mineral in the amygdales (filled vesicles) in the picture. Doppelganger and I would love to examine it in the hand, or better yet in thin section. I also thought of muscovite for the fan-shaped minerals, but I can't confirm just from the images. Muscovite forms thin transparent elastic sheets that split very easily. Large sheets of muscovite were used for the window in ancient parlor stoves, as well as in old candle lanterns. I think I still have my antique muscovite candle lantern. smile.gif

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PostFri Dec 22, 2017 1:01 pm 
This stuff is scattered around the top of Pueblo Mountain, in Oregon just north of the Nevada border. The rock is 4" across.

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Brushbuffalo
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PostFri Dec 22, 2017 2:10 pm 
Thanks for the picture, pcg. Interestingly, I drove by Pueblo Mountain this past July but didn't have time to do any exploring. The rock appears to be volcanic, probably a tuff breccia made of small rock fragments within a fine-grained matrix. But it could be a pebbly sandstone. I wish I could look at it in hand! 😁 Steens Mountain, a few miles north, is basalt, but the rocks in Nevada and the rest of the Basin and Range Province are highly varied. The white mineral is quartz. On the right is milky quartz, which is actually transparent but many microfractures dispersed throughout relect light, giving it the white appearance. Over toward the middle and left are many beautiful euhedral (excellent external crystal form) quartz crystals. Note their elongated prismatic form and on many you can see their hexagonal form on end. In this rock it is likely that the quartz formed after volcanism produced the igneous rock. The small bits of green are some sort of surface vegetation. Edit: Doppelganger has a valuable contribution, hypothesizing that the white mineral is natrolite, and I agree. See the posts on Dec. 28 and Jan. 3.

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pcg
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PostSat Dec 23, 2017 11:19 am 
Thank you. I'm surprised to hear quartz as I've never seen it look like this. If you ever get back to PM and have the vehicle and the nerve to take the road up to Ten Cent Meadow on the west side, that's where I found it, at the high point before heading down to the meadow - all over, even in the road. I'll never travel that road again unless BLM cleans it up with a bulldozer. At some point it will become impassable by even the foolish. Of course you could do the trip on foot as a long day hike as well.

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mike
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PostSun Dec 24, 2017 4:09 pm 
More of that rock below the summit of Pueblo Mtn. Someone thought it might be worth digging.

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pcg
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PostSun Dec 24, 2017 5:05 pm 
mike wrote:
...Someone thought it might be worth digging.
Yes, that looks like a small quartz deposit. I know there are some old mines/prospect holes on the east side, but we didn't explore that area. I'm curious to know what mineral they were hoping to extract. I'm guessing the sight of the white quartz had them thinking gold might be present? I think there are opal deposits around as well. I could spend weeks exploring that area.

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PostThu Dec 28, 2017 9:50 am 
I think a hardness test is in order. I'll do one as soon as I have time to round up a piece of glass.

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RichP
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PostThu Dec 28, 2017 9:10 pm 
This is kind of big, but I'm curious about this formation on Mt Wow on the southwest side of MRNP.
Rock on Mt Wow.
Rock on Mt Wow.

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