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Ammolite? Coal? Mica?


JIMMFinsman

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We find a lot of these washed up on the beach.  I've always thought they were coal from the few hundred shipwrecks off the coast the last several hundred years. Anyone know what this is?  Looks like an oil slick.  Very hard rock. Not scaly like Mica but I guess it could be. 

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  • Fossildude19 changed the title to Ammolite? Coal? Mica?
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If you want to identify it you might want to look up a some mineral and rock identification tests. I actually used the US highway administration's published guide to do some rock and mineral identification with some of my students (found at: https://highways.dot.gov/research/publications/infrastructure/FHWA-HI-91-025).

 

If it is coal it should streak on a tile or similar, be able to be etched by steel, and burn or smoke under flame, from what I remember.

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Thanks for that.   Ok--it does not mark like coal. Did not leave any mark. It is very hard and I tried to scrape with a steel nail and nothing. Burning had no effect. 

I think I mentioned we've found loads of coal pieces, practically every day you can find them here in the beach. This piece is not like the rest.   

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Also...I've had this piece for over 10 years and if it were Peacock Coal, which it looks like, shouldn't the iridescence be gone by now?  Once exposed to air it's supposed to disappear quickly.  

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Ok so it looks like this is most likely peacock coal. The outside has this hard irredescant crystalline layer. You can see in the pic where some of that is not covering the edges of the rock. I scraped in there with a nail and was able to scrape off basically coal dust.   I did burn it with a lighter until it got very hot but it did not ignite or burn in any fashion.  It held it's hear for about a minute. 

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4 hours ago, JIMMFinsman said:

 I did burn it with a lighter until it got very hot but it did not ignite or burn in any fashion.  It held it's hear for about a minute. 

So this in anthracite, no experience with anthracite, but it need a really high temperature to ignite / glow, as far as I know.

Franz Bernhard

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