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Author Topic: what type of rock is this?  (Read 3264 times)

Offline rocky15_nf

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what type of rock is this?
« on: 09/04/2012 19:44:48 »
I found this rock on a beach about 25 years ago. There were two this one and another smaller one but i have lost it over the years. It is not the type of rock around those parts. I have always thought that it was some sort of meteor. It does float. I live in Newfoundland Canada and have never seen anything else like this until last week when my brother dragged one up in a scallop drag in another area. Do anyone have any idea what this is.


 

Offline RD

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Re: what type of rock is this?
« Reply #1 on: 09/04/2012 20:39:35 »
« Last Edit: 09/04/2012 21:19:51 by RD »
 

Offline rocky15_nf

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Re: what type of rock is this?
« Reply #2 on: 09/04/2012 21:39:54 »
Thanks for your help now i know its not out of this world, lol.Just dont know how it got here as there are no volcanoes around here.
 

Offline RD

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Re: what type of rock is this?
« Reply #3 on: 09/04/2012 22:16:16 »
 

Offline Mazurka

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Re: what type of rock is this?
« Reply #4 on: 10/04/2012 12:25:11 »
It is reasonably safe to call it pumice.
I am not certain that it is possible to be so specfic as to call it vesicular basalt (although it could be) just from a photograph.  If I remember right, pumice tends to be  produced from more felsic rather than basaltic eruptions (which would also accord with the light colour) 

Pumice has been seen in "rafts" that have floated around for years.
 

Offline rocky15_nf

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Re: what type of rock is this?
« Reply #5 on: 10/04/2012 19:27:03 »
I dont know much about this, does pumice also come from volcanoes.
 

Offline Mazurka

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Re: what type of rock is this?
« Reply #6 on: 11/04/2012 12:37:30 »
Yes, "pumice" comes from volcanos.  It is actually a description of the texture of the rock rather than a description of the minerals in the rock*.  The holes (or "vesicles") are created by gases disolved in the hot lava and when it erupts the pressure keeping them disovled is relieved so it bubbles out.  (A bit like opening a bottle of lemonade) At the same time, the lava is cooling rapidly and the volcanic "froth" is frozen into pumice.   

Not all volcanos produce pumice - it depends on a number of factors including chemical composition of the lava and the amount of water and carbon dioxide in the mix.

*Some rocks are described by what they contain (for example granite contains quartz, mica and feldspar)  others by the grain size - siltstone, sandstone and gritstone are all mainly quartz, but appear quite different  and some by texture - such as pumice and porphyry.
 

Offline rocky15_nf

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Re: what type of rock is this?
« Reply #7 on: 11/04/2012 18:19:08 »
thanks for the info.
 

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Re: what type of rock is this?
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