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[Digest Post] Natural blue topaz?


#1

Dan, More on subject. About 3 years ago our G&M Society received a
huge donation of very old rough. Included were several bags of
tumble stones, small tuff - carnelian, red jasper, rose quartz and
beryl, etc. Most of the beryl was purely tumble or cab grade but
mixed in were a few handfulls of facet grade material. When I began
separating it, I did some SG and scratch tests and found thirty or
forty were actually topaz. Some were greenish, some yellowish but
many were light blue…all small in the 3-4 gm size but with cutable
areas. Don’t know origin but someone had a pretty good producing
mine somewhere.

Cheers from Don etc, etc. dcdietz@attbi.com


#2

One of the odd things about topaz is its ability to take on a
spectacular polish. I had a lecturer who claimed to be able to pick
out topaz blindfold simply by feeling it. So we put him to the test
and all the students brought in fairly hefty stones of various
materials - all over 5ct.

He could!
Tony Konrath
Gold and Stone
http://www.goldandstone.com


#3

Tony,

I suspect your professor friend could tell the difference not by
polish but by heft! A person who has rockhounded or handled even
rough stones for many years develops a very acute sense of how heavy
a particular kind of stone should be relative to its size.

For example, Topaz has an SG of 3.4-3.6 fairly heavy.
Glass is 2.2- 2.6 Very light
Beryl is 2.6-2.7 very light
Apatite is 3.1-3.2 still lighter than Topaz and distinguishable,
Even Spinel is 3.5 - 4 which makes it even heavier than Topaz.

While I always do scratch and SG tesdts to separate out like looking
stones, heft is a good first indicator what you have. Cheers from Don
at The Charles Belle Studio in SOFL where simple elegance IS fine
jewelry! @coralnut1


#4
 While I always do scratch and SG tesdts to separate out like
looking stones, heft is a good first indicator what you have.

Don, I surely hope you’re not doing scratch tests on cut stones, are
you? Destructive tests like that, while OK for rough, are usually
considered a bad idea on cut stones. Istead, might I suggest a
refractometer? Though they’re a little pricey, they’re easy to use,
and a highly useful test. But just a polariscope (which you can
build yourself if you like) will give you many of the seperations when
you combine it with SG, which you’re already doing. If you check SG
with heavy liquids, instead of the harder to use scales, you can
relatively easily make up liquids calibrated for specific
seperations, such as aqua from topaz, etc. Very fast to do, and no
damage to the stones that way.

Peter


#5

Peter, thanks for rounding this out a bit more. No…I’m not
scratching cut stones…I was referring to rough that sometimes
comes in unidentified batches.

I wish I had a refractometer…yes they are pricey! I do use
heavy liquids at times and also the polariscope (which I did build
myself). By the way, my hydrometer is one of the Hanneman direct read
out machines from Mineralab with is really quite easy to use. While
I know about all the intricacies of water temp etc, etc, using it in
a simple room temp mode will also give accurate enough read outs.

Thanks for the input, especially for our readers. Cheers from Don
at The Charles Belle Studio in SOFL where simple elegance IS fine
jewelry! @coralnut1