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Author Topic: What causes this colouration in a piece of slate?  (Read 923 times)

Offline maliyanjourney

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A mate handed me this to see if I could give an explanation of the coloration on the surface of this low grade slate. Apparently from a thin lens in a larger bed of folded (this bed at 90 deg) marine sediments (some of shallow marine volcanics) - hard to see in the photos i guess but I notices some cross bedding in one of the sub-layers of this specimen, I'm guessing of fan deposit.

The interesting bit is the coloration on the surface of fresh specimens. It has an 'opaline' or 'oil slick' appearance. Can't be seen when wet with water or lacquer. Crosses the layers within the specimen. Any suggestions!? Cheers!

Pictures hopefully attached

« Last Edit: 24/05/2016 08:28:58 by chris »


 

Offline RD

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Re: Colouration on slate lens
« Reply #1 on: 24/05/2016 05:56:48 »
 

Offline chris

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Re: What causes this colouration in a piece of slate?
« Reply #2 on: 24/05/2016 08:33:23 »
I think RD is right. The way the crystal has fractured leaves translucent layers of different thicknesses so light reflects from different depths and then interferes with itself, producing the colour patterns. If this is the case it's similar to why oil makes a rainbow on water.

http://www.thenakedscientists.com/HTML/questions/qotw/question/1000449/
 

Offline Bass

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Re: What causes this colouration in a piece of slate?
« Reply #3 on: 06/06/2016 19:09:04 »
I agree with RD. the color is from iridescence. Chris may be correct, or there could be minute amounts of iridescent minerals (iron or manganese oxides) that cause the color. Cross bedding suggests that there was some sort of current at the time of deposition.
If this is truly slate, then is likely that any fossil fuels would have been baked out of the rock.
 

Offline JimBob

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Re: What causes this colouration in a piece of slate?
« Reply #4 on: 29/06/2016 04:54:50 »
What about a diffraction grating ?
 

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Re: What causes this colouration in a piece of slate?
« Reply #4 on: 29/06/2016 04:54:50 »

 

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