WHAT IS THIS WHITE ROCK PLEASE?

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Offline mia531

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WHAT IS THIS WHITE ROCK PLEASE?
« on: 12/10/2012 14:49:22 »
FOUND THESE STONES ON A BEACH IN PANAMA. These stones have the white rock either as a layer towards the surface or as a filling in the middle. Some of the associated rock ( eg piece in foreground has lilac milky rock-what is that?) has an orange colour and orange or orangey pink crystals-what is the orange ? What is the white stuff, it is very dense and very white and smooth and hard. Hope someone can help?!

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Offline RD

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #1 on: 12/10/2012 16:35:02 »
« Last Edit: 13/10/2012 12:48:27 by RD »

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Offline Bill S

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #2 on: 13/10/2012 22:30:09 »
I think RD is probably right about the red-chert (jasper if you prefer), which would make the white stuff quartz.  The hardness is going to be diagnostic; it needs to be about 7.  If it's only about 4-5, you could have limestone/marble.  Go for it with a knife. :)

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Offline Bass

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #3 on: 14/10/2012 18:51:11 »
looks like typical vesicle filling and volcanic breccia cemented with chalcedony.  white is opal/chalcedondy (very fine grained quartz), I suspect the red is rhyolite or silicified rhyolite.
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Offline Bill S

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #4 on: 14/10/2012 19:52:13 »
No arguments from me, Bass; unless it's softish.  I used to have a specimen that looked very much like the large one in RD's post, but I could scratch it with a knife, and it fizzed a bit in warm HCl. 

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Offline mia531

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #5 on: 23/10/2012 19:09:37 »
Thank you all again for your responses.I have attached a close up photo as I'm not sure that the white resembles quartz...The solid white rock is very smooth and opaque. I looked up rhyolite which seems to be very granulated and unlike my sample...

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Offline Boogie

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #6 on: 23/10/2012 19:25:30 »
My monitor is giving me problems today, but it looks like banded agate or chalcedony as mentioned before.

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Offline Bill S

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #7 on: 26/10/2012 17:24:09 »
I think you are right to rule out rhyolite, although it is not always granular.  Obsidian is an amorphous form of rhyolite that is a natural glass.  However, itís hardness is rarely greater than 5.5, so, unless you can scratch your specimen with a piece of quartz, itís not obsidian.  Of course, Bass mentions silicified rhyolite; Iím not going to try to argue with that, except, perhaps to mention Ockhamís Razor.   :)

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Offline Lab Rat

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Re: WHAT IS THIS WHITE ROCK PLEASE?
« Reply #8 on: 11/01/2013 18:09:53 »
I agree that the top one in the second post looks somewhat like chalcedony.  I say this due to the "border" that goes around the outer edge.