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Rock crystal or glass?


#1

Greetings all,

I enjoy reading the Orchid Digest daily and have learned so much
from everyone here. I’ve not posted previously and hope I don’t
sound too idiotic.

I’ve just purchased a few 8mm and 10mm spheres (undrilled) of rock
crystal from a seller on Etsy, and intend to incorporate them into
some pieces to sell. I paid about $2 each and while they look really
pretty, I’m beginning to wonder if they’re really clear quartz or if
I just bought glass marbles. How can I tell the difference without
resorting to engaging a certified gemologist? They are "crystal"
clear (heh!), no visible inclusions or bubbles or seams. Though I’ve
made only a meager investment in this project I do like to be
absolutely clear (ok, enough w/the puns) about what I’m offering to
customers. As this is a nagging concern, I thought I’d ask the
experts.

Thank you in advance. I greatly appreciate all your information
sharing and guidance.

Regards, Patricia


#2

Patricia,

If you have a pair of polaroid sun glasses lying around, remove one
lens, preferably the lens for the non dominant eye. Put on the frame
which now has only one lens, and hold the other lens in front of the
lens you are wearing, maybe six or eight inches away. Look toward
thesun or a bright light source and rotate the lens in front of the
one you are wearing until it’s in the position where the least amount
of light comesthrough. Holding a sphere between the two lenses,
rotate it between your fingers, trying various orientations. If the
sphere shows dark and light as you rotate it, it is not glass. If you
have one that IS glass it will not change from light to dark. I would
think though that if you had a loupe or other magnifying device of at
least 10 power, you should be able to see somebubbles or kind of
"swirly" areas if it is glass. Good luck Jerry in Kodiak.


#3

That’s easy. I sold fine quality crystal balls for Ann and SI
Frazier in the 80s. They had m any flawless and near flawless ones
from a Canadian prewar stockpile, so I learnt from them that if I
rolled the balls in various directions on a white papers, just on top
of a thin black line, if it was quartz, the thin line would double at
some point. Try all directions, and do it slowly.

M J St. Amand


#4

Quick and dirty. do a scratch test

Quartz has a hardness of 7 and glass 4.5 to 6.5 so if you have a
piece of quartz with a sharp edge you can do a scratch test. Google
"hardness tables" and then google “hardness scratch” test for more
info

The harder substance will scratch the softer but not vice versa. In
theory quartz will scratch quartz but you will need to put a fair
amount of pressure, on glass it will put a scratch in it quite
easily.

Get a piece of glass and a piece of quartz and experiment :slight_smile: to get
a feel for it, then test your spheres.

Kay


#5

If you don’t mind sacrificing one, smack one with a hammer, glass
will bust apart like, well, glass. quartz will break a little
differently, maybe have some flat surfaces (cleavage planes).

Remember, safety first, double bag it!

But that’s just the start. Next, take a fragment of the broken
sphere and try to melt it with a propane torch, glass will start to
melt around 1400 to 1600 Fahrenheit while quartz melts at 3038 F. An
acetylene torch will melt quartz, a propane torch will not, even with
oxygen.

Have fun and break lots of marbles!


#6

Scratch test? Better ways than to do a test that causes damage. bad
advice!


#7

Smack it with a hammer? Not exactly acceptable in the gem world. In
addition it will only tell you about the one you have destroyed, not
the restof them. One way unscrupulous gem dealers increase their
bottom line is bysalting parcels of naturals with cheaper synthetics
or fakes, so to check them all you would have to destroy all.
Counter productive, I’d say, eh?

Jerry in Kodiak


#8

And by the way, a scratch on a transparent sphere will appear much
larger onthe opposite side.


#9

glass will have bubbles under a microscope.


#10
glass will have bubbles under a microscope. 

Often, yes. But not always. (example: try to find bubbles in window
glass…)

Combine the microscope with a polariscope and you’re on more solid
ground. Plus, worth nothing that the microscope will see a lot more
than just bubbles.

Conchoidal fractures in tiny chips, the melty or molded surfaces on
those types of glass, the degree of polish/luster, and more. With
some experience, glass is usually pretty quick and easy to I. D.
Often, a loupe is quite enough. But the experience of what to look
for is the really important instrument, above the microscope or
polariscope. [for the OP] If you can, sign up for the GIA gem
identification course or something similar. Then issues of what are
you being sold are no longer a problem. You’ll know.


#11

Regarding gemology courses, education is always helpful. The GIA
course or the FGA cert (UK) or Canadian Gemology Assn. course are all
great for learning and giving you a recognized certificate. However,
if all you are after is gemology knowledge and you don’t have a need
for a certificate, there are a number of on line schools and even
some free on line courses (such as Barbara Smigel’s very nice
offering). You can also teach yourself gemology either on line or
through books. As I stated in another thread, if you can read through
and thoroughly understand Hanneman’s book, Affordable Gemology,
you will know more than most GIA graduates and be able to ID and
separate gems without expensive instruments, which look nice in your
office or store, but aren’t necessary from most ID.

I say this as someone who completed the GIA gemology course in 1996
and also did a lot of self-study. While I learned some things from
the GIA course, my study of books before and after that actually
taught me just as much. As I mentioned in the recent earlier thread,
Antoinette Matlins’ book, Gem ID Made Easy, is a great starting
point.

As to glass, yes, window glass doesn’t have bubbles, but who makes
gem imitations out of it.

And glass does have a concoidal fracture, but so does quartz. If you
use enough magnification, most natural gem materials have inclusions.
Yes, glass often has telltale bubbles or swirls.

Also if it’s old, it will have a lot more wear than quartz and is
warmer to the tongue than crystalline materials. In a faceted stone,
the rainbows seen when the stone is held up to the eye will
differentiate quartz from glass. Glass will show one single rainbow
with the colors in a typical row (ROYGBIV). Quartz, being
birefringent, shows two overlapping rainbows, which look a little
different. This is part of the Hanneman-Hodgkinson method of gem ID
without instruments.

Good luck with gemology, it’s fun!