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Identity HelpDiamond or Quartz?

16th Sep 2015 07:59 UTCAnonymous User

08020360016027093456904.jpg
Copyright © mindat.org
Hello Experts,


Please could you help me identify if this is a diamond or quartz? It's a very small stone found in Andhra Pradesh (India) weighing just 1.5 ct. I am bit sceptical to carry out any scratch test on this stone :-). I'll get it tested in the laboratory in couple of weeks but if you could provide your expert views, that would be very helpful.


Many thanks.



07245100015669295401893.jpg

16th Sep 2015 11:35 UTCJean-Louis O.

Try to scratch an aquamarine with it if you have one.

16th Sep 2015 12:25 UTCOwen Melfyn Lewis

Why must it be either diamond or quartz? From your pics, it might be one of several other minerals.


Topaz?


What's its SG?

16th Sep 2015 12:54 UTCJolyon Ralph Founder

We can't identify a rounded grain from a photo. You need to take it somewhere for professional testing.


Sorry, but we can't really help any more on this.

16th Sep 2015 13:00 UTCMatt Courville

If this was diamond, you should be able to scratch any other mineral with it with no damage...unless I'm overlooking something. If it's quartz, there is no real loss I would feel for that sample. The conditions on where/what type of rock it was found in will help narrow it's identity down also. I think Owen's suggestion to do a specific gravity test will be worth setting-up(buying a balance/scale) if you plan on getting many more like this one.


Cheers,

Matt

16th Sep 2015 13:08 UTCBob Harman

HEY EVERYONE, JOLYON IS CORRECT!!!! This is a tiny 1.5 carat stone. Scratch tests?? Specific gravity?? Come on, tell the poster to have it examined IN PERSON by an ethical gemologist or other expert. CHEERS......BOB

16th Sep 2015 13:19 UTCMatt Courville

I didn't catch that Bob - for less than 1/2 gram sample I completely agree. These diamond post seem to happen a lot, but I think it gets new people excited about minerals in general, which seems positive I would think:-)

16th Sep 2015 14:04 UTCOwen Melfyn Lewis

Oh bob......


Speaking as an unethical gemmologist, I'd advise RB to acquire the means (equipment and knowledge) to make some simple tests himself before paying that 'ethical gemologist' a handful of dollars to tell him what he can find out fairly simply for himself, if he is so minded to equip himself and to learn. I.e. is this a diamond or not? That's a much easier task that identifying what the specimen actually is, to be sure of which might, in the end, require some advanced quantitative testing. Positively identifying a rough diamond is a relatively simple task (given knowledge, etc.).


1.5 ct is actually larger than a dozen or so in my collection from around the world and larger too than almost all the others that I have examined. Whether ethical or not, a good gemmologist will be happy working with diamond both cut and rough down to 0.01 ct in size


As regards the photos of this specimen, I have already said (gently) that I can't tell what it is from the pics and nor, as Jolyon says, can anyone else. However and just off those pics I will bet a large beer that the specimen is not diamond and I would not feel it a good investment to spend 25 - 50 bucks (plus postage etc, in getting a better informed opinion. However, if Rekha Bhat wishes, I'm happy to do some testing and photomicrographs that should provide an authoritative opinion without charge and for just payment of the return postage.


Anyone else spot the 'not a diamond' hints in the pics?

17th Sep 2015 13:50 UTCAnonymous User

Thank you all for the advise. I would be taking it to a lab soon. However, I did try conducting specific gravity test at home and it reads 3.6


Any further clues.....could it be topaz?


Thank you very much.

17th Sep 2015 16:45 UTCOwen Melfyn Lewis

It looks as though your specimen has been well cleaned and that one sees some form of wrinkled skin or rind over over crystal underneath. There is one (possibly two) place(s) where the crystal under the rind is visible. This is not an appearance that I have ever seen in a rough diamond and does not look at all right to me.


The specimen looks heavily water-worn (as can be diamond) but the crystal forms of diamond usually withstand wear much better than this specimen has, being quite worn down.


Even in the rough, diamond should show an adamantine lustre. I can't see that at all in your pics. However, the lighting angle and slightly soft focus are unhelpful here.


In sum, I would expect an expert examination to confirm that this is not a diamond. But, as said, identifying what it is may be a more difficult task (and not worth the cost unless it *is* a diamond). It can't be identified from the pictures. Topaz is one possibility, but one would need more compelling evidence that just an SG determination of 3.6 to form an opinion.


Have you checked your equipment and method of SG determination for accuracy? The smaller the specimens you work with the more accurate your balance and method need to be. You need to be certain that you can always determine an SG accurate to two decimal places at the smallest size of specimens that you work with. For your present purposes you can do this as follows:

- Break off a small piece of clean rock crystal (monocrystalline quartz) that weighs 1 to 2 ct. This will (to 2DP) have an SG of 2.65 as all rock crystal does that is clean, transparent and has no major inclusions.

- With your balance and method of SG determination. Determine the SG of your test sample of rock crystal three times.

- If all three determinations give to a value for SG that lie in the range 2.64 - 2.66, then your equipment and method are fine to make SG determinations of specimens as small as is your quartz test piece.

- If one or more of your SG determinations for this quartz sample lie outside the 2.64 - 2.66 range, then add together your three determinations and divide the total by 3 to give you a mathematical average. If the averaged value is within the acceptable range, then you can use your equipment and method for samples of 1-2 ct size but will need, each time to make three pairs of measurements and to average the three SG results obtained.

- If even an averaged SG result for rock crystal lies outside the 2.64 - 2.66 range, then you need a more accurate balance (and/or SG determination method) to correctly determine SGs for specimens as small as 1-2 ct.


Like rock crystal, clean and unincluded diamond monocrystal also has a very reliable SG and should always be in the range 3.51 - 3.52. However, if the specimen is translucent to opaque results may be useless as the specimen is not pure. The SG of clean topaz should lie in the range 3.39 - 3.57 which completely overlaps the SG range for diamond. Accordingly SG is not a suitable test for differentiation from topaz. However there is no other *colourless* crystal that has the same SG as diamond and differentiation between diamond and topaz is quite simple.


When you have your specimen tested, please do let us know what the result of the testing is. It is always interesting to get to the bottom of these little puzzles :-)
 
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