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That 65 carat 'zircon'

Posted: Sun Feb 12, 2017 11:34 am
by blisters
Well...... we got back home and did set specific gravity test on that stone and guess what it is not a zircon.

The test went as follows.
12.95 grams dry weight and into the 4 degree water.
Wet weight was 7.55, so the difference is 5.4.
12.95 รท 5.4 gives us 2.39

The only mineral that we can come up is Petalite with a SG of 2.39.
Attached is some more pics and info, and so we would be interested in hearing opinions!

Re: That 65 carat 'zircon'

Posted: Sun Feb 12, 2017 3:11 pm
by digginhard
looks technical to me mate.Sorry all went a miss and I missed you guys the other day.Anyways I just wanted to let you know I picked up a 50ct zircon the other day with another 100 or so weighing at least 1-10ct out of one hole in a filthy little creek.Pics and weights to come.

Re: That 65 carat 'zircon'

Posted: Sun Feb 12, 2017 8:11 pm
by blisters
Cheers digginhard. No worries at all mate, looks like your looking in the right places and our paths will cross some time!

Re: That 65 carat 'zircon'

Posted: Wed Mar 08, 2017 10:15 pm
by zzeehan
Hi pan4blisters,
Looks like a nice stone either way. Was wondering about the accuracy of the scales you were using to determine the SG?
A stated accuracy of 0.01g for any scales you intend using is what you are after, but remember, just because the scales have a LCD display showing two decimal places doesn't necessarily prove an accuracy of the same. Also, if your scales are a bit clunky or weren't calibrated it would be easy for your first decimal place to wander, too.
Your technique seems pretty good, I do see a lot of people doing SG's the hard way though. A simpler and accurate method requires an accurate carat scale, a small beaker/glass of water, a calculator and some fine cotton. See below.

Weigh your stone (aquamarine in this case): 2.06g
Tie some cotton to it
Zero a beaker of water on the scales
Measure the weight of the water displaced by totally immersing stone supported by cotton, just below surface, not touching anything: 0.76

Divide 2.06 by 0.76

Answer: 2.71

Walter Schumann, Gemstones of the World, says for aqua SG: 2.68 - 2.74
Bang in the middle.

Petalite has a perfect cleavage which you should see at least some evidence of in your stone when viewing with a 10x loupe.
If you are keen, try the SG technique above to confirm/disprove your previous calculation.


Re: That 65 carat 'zircon'

Posted: Mon Mar 13, 2017 9:03 am
by blisters
Hi Zzeehan. Thanks for that much simplified method of doing the S G test, i thought there must be an easier way of doing it! :roll: I'll check the scales!

Re: That 65 carat 'zircon'

Posted: Fri Mar 17, 2017 11:21 am
by zzeehan
No worries, Keep It Simple as they say!
Try some cotton, lol.