How is the identity of an unknown mineral determined?

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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 »

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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 »

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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 »

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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...
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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......

[attachment=5346]

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

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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  [:)]

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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

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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
The mind is like a parachute. It works best when open.  -- A. Einstein

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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
frethack

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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?
"It has been said that the primary function of schools is to impart enough facts to make children stop asking questions. Some, with whom the schools do not succeed, become scientists." - Schmidt-Nielsen "Memoirs of a curious scientist"

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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!
The mind is like a parachute. It works best when open.  -- A. Einstein