181lizard
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Post by 181lizard on Jul 20, 2006 14:24:10 GMT -5
Is it ok to post pic here if you want help identifying a rock? If not, let me know where... I dug this one out in my neighborhood. Best I can tell is it's a hunk of Chalcedony. (looks very much like a pic in a rock & mineral book I have.) It has the darker skin with the very milky inside. Lots of fractures at the open end which I hope don't go all the way through cause I think I'll have it cut. But I love the little specks inside.
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Sabre52
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Me and my gal, Rosie
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Post by Sabre52 on Jul 20, 2006 21:20:21 GMT -5
Yep, chalcedony and almost carnelian ( if it were more red or orange). Looks like a nice nodule that formed in a gas pocket in basalt or andesite. Scientific term is an amygdaloidal nodule ( meaning "almond shaped".....mel
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181lizard
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Post by 181lizard on Jul 21, 2006 0:40:22 GMT -5
That's fantastic info Mel! Although I'm puzzled by the "basalt". And, what would be andesite? I realize rocks can travel great distances from ancient glaciers, but where I dug this up at is the same area I get 90% of my rocks. Very mysterious!
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181lizard
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Post by 181lizard on Jul 25, 2006 11:59:47 GMT -5
This is another piece of chalcedony I think. About the same size as the previous one but a different color. This one is more golden/amber looking and has some material inside it. (it's the whitish globs you see) Both came from the same general area.
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Sabre52
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Me and my gal, Rosie
Member since August 2005
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Post by Sabre52 on Jul 26, 2006 9:49:37 GMT -5
Lizard: Andesite and basalt are a couple of the common type base volcanic rocks in which amygdaloidal nodules usually develop, Both are quite common in the west and a very probable origin for the agates you are finding. Like the Lakers that are the same sort of nodule, they were often transported huge distances by glacial or river activity. Nodules very similar to what you're finding occur in place at many locations in British Columbia ( for example the Monte Lake Beds), so it would not be unusual to find them transported to your area even if those volcanics don't occur locally however, I do believe your region is fairly rich in volcanic substrates......mel
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181lizard
Cave Dweller
Still lurking :)
Member since December 2005
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Post by 181lizard on Jul 26, 2006 20:37:31 GMT -5
Thanks for the info Mel... when soemone speaks about basalt, well normally you'd think of the beautiful basalt cliffs in the Gorge or like the ones I saw on my drive to St. Helens a couple of days ago. So when you talk about the area I live in, it's harder to imagine these nodules forming in same. (cause it's pretty much just dirt - hills - a few creeks) that type of thing. I'm gonna check into classes at the university next to us. There's got to be geology or earth science there & I would love to learn more!
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Sabre52
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Me and my gal, Rosie
Member since August 2005
Posts: 20,466
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Post by Sabre52 on Jul 27, 2006 0:14:34 GMT -5
lizard: Not all basalt contains agate nodules. In my experience the columner forms like you see in a lot of dramatic cliff formations frequently do not. I believe the type known as vesicular basalt that contains lots of gas pockets is the more likely type for agate as these vesicles or pockets are filled by the silica to form agates or geodes......mel
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