Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: dong on 23/11/2008 06:58:21

Title: How is the identity of an unknown mineral determined?
Post by: dong on 23/11/2008 06:58:21
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?
Title: Re: How is the identity of an unknown mineral determined?
Post by: RD 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
Title: Re: How is the identity of an unknown mineral determined?
Post by: blakestyger on 23/11/2008 11:02:15
If you've got the kit, I imagine that refractive index should help separate some minerals.
Title: Re: How is the identity of an unknown mineral determined?
Post by: Bored chemist on 23/11/2008 13:16:58
If you happen to have an X ray diffractometer...
Title: Re: How is the identity of an unknown mineral determined?
Post by: Bass on 23/11/2008 17:05:51
The easiest way to distinguish quartz from calcite......

 [ Invalid Attachment ]

clacite has it, quartz doesn't
Title: Re: How is the identity of an unknown mineral determined?
Post by: Bored chemist 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.)
Title: Re: How is the identity of an unknown mineral determined?
Post by: Bass on 23/11/2008 21:06:57
Cleavage- calcite has it, quartz doesn't
Title: How is the identity of an unknown mineral determined?
Post by: frethack on 24/11/2008 01:07:25
This is certainly an example of calcite because the cleavage is perfect.
Title: How is the identity of an unknown mineral determined?
Post by: RD 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  [:)]
Title: How is the identity of an unknown mineral determined?
Post by: Chemistry4me 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
Title: How is the identity of an unknown mineral determined?
Post by: JimBob 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
Title: How is the identity of an unknown mineral determined?
Post by: frethack on 07/12/2008 08:26:46
This is your girlfriend, Jim? 

I know how you like to share!....hehehehhe
Title: How is the identity of an unknown mineral determined?
Post by: techmind 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?
Title: How is the identity of an unknown mineral determined?
Post by: JimBob 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!