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Author Topic: What is the difference between slate and shale?  (Read 17557 times)

mattmckee

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What is the difference between slate and shale?
« on: 24/06/2009 14:23:56 »
Hi, in our school we have some slate, and we think some shale, but we can't agree on how to tell the difference in a practical way for our science technicians, or teachers.  I thought shale was softer, and more brittle, but some labelled bags we have seem very similar.   I've read one feels softer when wet, and smells more mud like, but is there a more reliable way...   Any suggestions.

Also is it just a matter of how much heat and pressure - so shades of grey, rather than a definate boundary of that IS shale and this IS slate?

Cheers

Matt ? ? ? ? ???
« Last Edit: 23/07/2009 20:57:48 by chris »

Bass

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Re: What is the difference between slate and shale?
« Reply #1 on: 25/06/2009 04:09:08 »
I always used what I call the "tink" coefficient.  Take a flat piece in your hand and tap it lightly with your hammer or other hard object (but not hard enough to break it). 

Slate goes "tink", shale goes "thunk".  Any your right, shades of gray.  Shales gradually harden as mineral changes during metamorphism, creating slates.

Then there's the whole argillite thing...

mattmckee

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Re: What is the difference between slate and shale?
« Reply #2 on: 25/06/2009 08:55:50 »
Thanks, that's reassuring, if not the easy answer I'd have preferred.
In discussion since we wondered about the clarity of the layers and colour;
 if its got clear and 'splittable' looking layers is it more likely to be slate?
 if its darker in colour is it more likely to be shale?

Cheers

Matt :-\

JimBob

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Re: What is the difference between slate and shale?
« Reply #3 on: 25/06/2009 16:19:08 »
Again, gradation. I have seen layers - and the LACK of layers - in both

Ophiolite

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Re: What is the difference between slate and shale?
« Reply #4 on: 25/06/2009 19:06:55 »
Both slate and shale are fissile. They split along planes in the rock. In a shale these planes are the bedding planes of the rock. These mark out the individual layers of clay that were laid down as sediment. In the slate these planes are mineralised layers oriented in response to a regional stress field during low grade regional metamorphism. These planes may be parallel to the bedding planes, but more likely are not.

Jimbob, I would call a 'shale' with no obvious fissility a claystone. But then I recall many an argument with colleagues over whether a sample was a greyish-green shale, or a greenish-grey shale. And once we'd settled that someone else would say it was gray, not grey.

 

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