GeologyRocksHelp ID Montana, USA rock found in creek
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The 'lump' has two
Mon, 08/20/2012 - 17:15The 'lump' has two possibilities. It looks very much like a volcanic tuft - ash really, which has fallen into water (hence the wavey band). We have a similar thing over here at Borrowdale in the Lake District, but it cleeves easily and is used for roofing slates, accounting for the green roofs in that part of the world.
However, it looks like there is a vug (cavity) with darkish green crystals in (although they are out of focus) which could be olivinite. In which case it is a plutonic igneous rock, although I've never seen that colour before. In itself not very valuable, but those crystals (if I am right) when gem quality are called peridote.
But it could also be furness slag.
The specimens in the jar look like they might be fluorite. When you pick them up do they feel heavier than you would expect?
Funny thing is that you say you found them in a creek. Therefore I would expect them to be more rounded.
I am assuming that MT is Montana, and I have no idea of the geology there. It might be better to take some decent photos when you get home and post them.
John
“Civilisation exists by geological consent, subject to change without notice.” - Will Durant
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I can't tell what the green
Tue, 08/21/2012 - 13:18I can't tell what the green one is. Maybe if I could examine it in person. Maybe rhyolite, maybe mudstone, maybe something else.
The specimens in the bottle look like quartz to me. The big round one in the middle of the bottom picture has a very slight tint of amethyst to it.
I'm not sure, but I think there are some pay to dig saphire sites in Montana. If you are still there, you might do a quick internet search and go check one out.
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Help ID Montana, USA rock found in creek
Submitted by MTMAN on Mon, 08/20/2012 - 04:43.Hello, I found the following rocks which caught my eye in a creek while on vacation in MT, USA. I was wondering if you would be able to help me identify it. It appears to have speckled crystals in the blue section which reflect light when rotating the rock around. The outside appears grey in color. Sorry for the poor quality, still on vacation and only had a cellphone. Nearby I sifted through the gravel and found the following smaller rocks. One of which is completely transparent (3rd from the right) reminding me of sapphire hunting for fun at a commercial mine. Others have portions of transparency but otherwise cloudy. If you could help me ID these as well that would be super! Thanks!
MTMAN