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Author Topic: How is the identity of an unknown mineral determined?  (Read 17255 times)

Offline dong

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I have two questions, could you please give me your opinion ?

Which ones are most useful in discriminating between minerals that look like the similar?
Describe a strategy that would allow you to determine that an unknown clear calcite crystal is indeed not the same as a known clear crystal of quartz?
« Last Edit: 23/11/2008 21:57:28 by chris »


 

Offline RD

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Re: How is the identity of an unknown mineral determined?
« Reply #1 on: 23/11/2008 08:03:10 »
Calcite will fizz in weak acid , quartz will not.

If the quartz is pure it will be much harder than calcite, (i.e. calcite will be more easily scratched). http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness#Intermediate_hardness
« Last Edit: 23/11/2008 08:16:02 by RD »
 

blakestyger

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Re: How is the identity of an unknown mineral determined?
« Reply #2 on: 23/11/2008 11:02:15 »
If you've got the kit, I imagine that refractive index should help separate some minerals.
« Last Edit: 23/11/2008 22:57:13 by blakestyger »
 

Offline Bored chemist

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Re: How is the identity of an unknown mineral determined?
« Reply #3 on: 23/11/2008 13:16:58 »
If you happen to have an X ray diffractometer...
 

Offline Bass

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Re: How is the identity of an unknown mineral determined?
« Reply #4 on: 23/11/2008 17:05:51 »
The easiest way to distinguish quartz from calcite......



clacite has it, quartz doesn't
« Last Edit: 23/11/2008 17:08:18 by Bass »
 

Offline Bored chemist

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Re: How is the identity of an unknown mineral determined?
« Reply #5 on: 23/11/2008 19:20:43 »
I don't see how that picture shows "the ability to make 2 images of one object" (calcite has it, quartz doesn't).

http://en.wikipedia.org/wiki/Iceland_spar

But I'm prepared to look at it until I do understand.
(Incidentally, from my point of view, I have a better chance of getting my hands on an X ray diffractometer.)
 

Offline Bass

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Re: How is the identity of an unknown mineral determined?
« Reply #6 on: 23/11/2008 21:06:57 »
Cleavage- calcite has it, quartz doesn't
 

Offline frethack

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How is the identity of an unknown mineral determined?
« Reply #7 on: 24/11/2008 01:07:25 »
This is certainly an example of calcite because the cleavage is perfect.
 

Offline RD

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How is the identity of an unknown mineral determined?
« Reply #8 on: 24/11/2008 03:26:00 »
This is certainly an example of calcite because the cleavage is perfect.

I suspect a high silicone content  :)
 

Offline Chemistry4me

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How is the identity of an unknown mineral determined?
« Reply #9 on: 28/11/2008 03:01:38 »
This is certainly an example of calcite because the cleavage is perfect.

I suspect a high silicone content  :)

HAHA...LOL
 

Offline JimBob

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How is the identity of an unknown mineral determined?
« Reply #10 on: 01/12/2008 21:16:29 »
This is certainly an example of calcite because the cleavage is perfect.

No need to laugh, they are real. I sent Bass this picture of my girlfriend and he cropped it to emphasize the geological point to be made. (Notice the plural.)
 
I suspect a high silicone content  :)

HAHA...LOL
 

Offline frethack

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How is the identity of an unknown mineral determined?
« Reply #11 on: 07/12/2008 08:26:46 »
This is your girlfriend, Jim? 

I know how you like to share!....hehehehhe
 

Offline techmind

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How is the identity of an unknown mineral determined?
« Reply #12 on: 08/12/2008 00:07:52 »
I have two questions, could you please give me your opinion ?

Which ones are most useful in discriminating between minerals that look like the similar?
Describe a strategy that would allow you to determine that an unknown clear calcite crystal is indeed not the same as a known clear crystal of quartz?


X-ray diffraction is the catch-all way to do crystallography (but the machine is likely to be at least as big as a washing-machine and cost a lot more).

Quartz is often found naturally growing as hexagonal-cross-section rods (not uncommon in some areas of Wales). I don't know what shape your unknown calcite might be.

Quartz is piezoelectric, so if you deposit some metal electrodes on it and apply a high voltage you can make it move fractionally (audibly click).

If you bash two lumps of quartz together in the dark you get a yellowy flash of light from them (and a strange smell). I've seen this with polycrystalline quartz, like the white pebbles you get on the beach.

Because of the piezo electricity, if you hit quartz with a hammer in the dark, you might get to see some sparks? Or just squeezed some in a vice, then released it again?
 

Offline JimBob

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How is the identity of an unknown mineral determined?
« Reply #13 on: 09/12/2008 02:14:05 »
This is your girlfriend, Jim? 

I know how you like to share!....hehehehhe

Forgive him.

He is still but a child - and will remain so all his life. He amuses so easily!
 

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How is the identity of an unknown mineral determined?
« Reply #13 on: 09/12/2008 02:14:05 »

 

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