Li0nh3eart
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Fragments of Geology
It's not the greatest of thread titles, but it's the best I could come up with.
Firstly I would like to skim over something that made immature people (i.e. me a year ago) giggle. This is slaty cleavage.
This occurs in incompetent rock (rock that flexes under compression) that contains platy minerals (e.g. clay, mica). When compression is put upon the rock, the rock folds and the platy minerals align themselves perpendicularly to the direction of force to minimise resistance. The cleavage also aligns itself parallel to the axial plane (the line that bisects the fold) of the fold.
Think of it like spaghetti strands. If you push against them, the strands will align themselves at 90 degrees the direction you're compressing them in.
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Apr/13/2011, 18:12
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Morwen Oronor
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Re:
Interesting Leo, have you got pictures to show us of some examples. I think I know what you're talking about. Maybe you could demonstrate with a picture.
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Apr/14/2011, 6:27
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Petal Alderin
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Seems like an irresistible force meeting an immovable object, clearly defined. Although you say the rock is flexible, so maybe not, on second thoughts! I would think that the incompetent rock must still be extremely hard and only can be compressed by something very strong, so the platy minerals must be stronger than I thought - I was always under the impression that clay was fairly soft?
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Apr/14/2011, 17:42
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Li0nh3eart
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Re: Re:
Clay is soft, but it doesn't fracture under force (try it for yourself if you wish), it bends, hence why it's good for moulding. Of course if you put it under extreme force it will eventually break into two, but it's not like limestone which fractures under minimal compression. Platy minerals are just minerals that can align themselves due to them being elongated.
MO: I've looked for suitable diagrams on the net, but I can't find any clear ones. I'll keep looking though.
Last edited by Li0nh3eart, Apr/15/2011, 17:27
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Apr/15/2011, 17:26
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Petal Alderin
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Clay soil in the garden is quite easy to break up into smaller lumps though?
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Apr/15/2011, 17:33
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Li0nh3eart
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Re: Re:
It doesn't fracture though. If you look at a rock outcrop of limestone or sandstone vertical fractures (joints) can often be seen, but if you look at an outcrop containing clay (i.e. shale) there will be no jointing.
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Apr/15/2011, 17:42
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Morwen Oronor
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Interesting Leo. Keep looking for images. Maybe take your camera and get some of your own.
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Apr/15/2011, 19:52
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Petal Alderin
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It's very interesting ... I just find it difficult to identify the different types of material, rocks etc - apart from the most obvious, that is. No doubt it comes with time and practise and familiarity.
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Apr/15/2011, 20:44
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Morwen Oronor
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Which is why I think Leo should take photos of what he wants to teach us so he can show us what he's talking about and we can learn the differences.
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Apr/16/2011, 6:28
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Li0nh3eart
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Re: Fragments of Geology
I did see a flute cast while on the walk yesterday. I did think of taking a photo, but it was far away and very difficult to get to. I wish I tried now! :banger2:
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Apr/17/2011, 20:38
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