is this amythist stuck on a rock?

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Anastasia.fr.1

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is this amythist stuck on a rock?
« on: 08/08/2009 18:02:50 »
the top is like gem stones and the bottom is just like a normal rock. do you think that the top is the amythist and the bottom is just a plain rock?

The rock is grayey blue with a green bottom witch looks abit like a moss stain

Bottom
[attachment=9376]

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Anastasia.fr.1

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is this amythist stuck on a rock?
« Reply #1 on: 08/08/2009 18:03:33 »
Top
[attachment=9378]

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Anastasia.fr.1

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is this amythist stuck on a rock?
« Reply #2 on: 08/08/2009 18:04:33 »
side
[attachment=9380]

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Offline Chemistry4me

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is this amythist stuck on a rock?
« Reply #3 on: 09/08/2009 00:29:00 »
I think that is just the way they are found.


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Offline traveler

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is this amythist stuck on a rock?
« Reply #4 on: 09/08/2009 08:14:44 »
Looks like it's from Brazil.

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Offline JimBob

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is this amythist stuck on a rock?
« Reply #5 on: 09/08/2009 16:31:51 »
Anastasia, This is a beautiful specimen of a geode. These are formed when silica-rich water moves through rocks. These crystals form in a hole often formed by an air bubble in a volcanic rock. The place where these formed in lava or shallow subsurface volcanic rocks after an eruptive episode through older sedimentary rocks. From the minerals seen in this rock we can guess that the rocks there before the eruption or volcanic episode were probably sedimentary, probably having a good deal of limestone and dolomite layered in them. Limestone and dolomite are composed of calcium carbonate and calcium-magnesium carbonate, respectively.   



The first of these crystals formed in the bubble was a copper ore formed probably of malachite (1 - the green crystals), a copper carbonates. Deposited around these is a layer of azurite (2 - the blue layer) which is probably dissolved malachite that was deposited in a slightly different form on and around the malachite mineralization. Then very hot water began dissolving other minerals besides just the copper minerals These other minerals are a bit more difficult to dissolve. They are also darker in color so the layers that were formed in the water are darker. A small layer of possibly calcium rich minerals were laid down (3) and then more alternating layers of light and dark non-crystalline silicate were formed in this cavity (4.)

Finally, as the water flowing into this bubble first normal quartz, then as the quartz began to grow larger, iron and silica was added in an complex but organized way into the crystal structure to form the purple color of amethyst.

Amethyst has been known for a long time and is found all over the world. Russia has the deepest purple colored of all amethyst occurrences.

« Last Edit: 09/08/2009 20:53:49 by JimBob »
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Offline Chemistry4me

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is this amythist stuck on a rock?
« Reply #6 on: 10/08/2009 04:33:57 »
Great analysis, I wish I could do that one day [;D]

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Offline Bass

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is this amythist stuck on a rock?
« Reply #7 on: 10/08/2009 06:15:50 »
Wrong green color for malachite- not sure about azurite either.  Green may be zeolite?  zeolites are common mineral fillings in volcanic vugs.
« Last Edit: 10/08/2009 06:17:49 by Bass »
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Offline Chemistry4me

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is this amythist stuck on a rock?
« Reply #8 on: 10/08/2009 06:23:57 »
Whoops [;D] Did I speak too soon?

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Offline Karen W.

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is this amythist stuck on a rock?
« Reply #9 on: 10/08/2009 09:05:04 »
Wrong green color for malachite- not sure about azurite either.  Green may be zeolite?  zeolites are common mineral fillings in volcanic vugs.

I have seen green malachite about that color..
I can"t remember if it was from Mexico or where?

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Offline Karen W.

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is this amythist stuck on a rock?
« Reply #10 on: 10/08/2009 09:07:28 »
Top
[attachment=9378]

WOW...Those are Gogeous Anastasia! Thunder eggs are so pretty!

Jim bob are the Geods the same as what we here call a Thunder egg?

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Offline traveler

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is this amythist stuck on a rock?
« Reply #11 on: 10/08/2009 11:16:56 »
Geodes and thunder eggs are pretty much the same except that geodes are hollow.

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Offline coquina.rocks

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is this amythist stuck on a rock?
« Reply #12 on: 09/09/2009 11:24:01 »
Wrong green color for malachite- not sure about azurite either.  Green may be zeolite?  zeolites are common mineral fillings in volcanic vugs.
The green appears to be the color of aventurine.

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Offline JimBob

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is this amythist stuck on a rock?
« Reply #13 on: 09/09/2009 20:29:33 »
It could be. Makes sense if the trace minerals in the clays produce a green color - iron for example
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