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Identifying
Stones
One of the most interesting and challenging
questions a retailer of semi-precious gems is confronted with
is "what stone is this?"
Often the answer is an easy one, either because the stone
was ordered specifically by specimen or because it is an easily
identifiable species of a particular mineral. For example
amethyst
is easy to identify because of its purple coloring and relative
transparency.
But what
about that silver ring with the unusual and beautiful stone
you got as part of an assortment from Whirled
Planet? Being able to determine the correct stone classification
will make the sale easier and will enhance the purchase from
the customer's perspective. Most people learn to identify
stones through experience. Familiarity with stone types breeds
confidence and a working knowledge that can be added to gradually
over time.
Some background
information is helpful however. Gemologists use several methods
to determine a stone type. First and foremost they use primary
color as a reference point. Some minerals like azurite
or malachite
are very consistent in color from specimen to specimen. Other
gems like quartz are harder to classify because they come
in all colors, depending on what trace minerals are present.
Purple amethyst is a kind of quartz with iron present, while
rose quartz gets its color from titanium.
Color
can also be altered, as it has for millennia, to improve or
change the appearance of a stone. Most commercial citrine
is actually heated amethyst. In this same category of classification
method we can apply the idea of "grain" or texture.
The banding found in various agates, or the crystalline nature
of various quartz colors lends a certain character to each
that is consistent over various colors. The similarities between
rainbow
moonstone and labradorite
are an easily identifiable example of similar feldspars that
have completely different primary color.
Gemologists
also refer to "streak color" as a means of determining
species. Basically, this involves scratching the stone with
moderate force on unglazed porcelain as found on the bottom
of a dinner plate or floor tile. The color of the streak on
the ceramic shows the true color of the stone minus the impurities
that cause the coloration. Blue
sodalite, for example, will scratch white. This test is
used for testing stone rough and will damage set stones, so
don't try this with anything you plan to sell! I mention it
here for reference purposes only.
Another
method gemologists use to classify gems is by testing their
hardness. In the 1800's the Moh's hardness scale was developed
to stratify all the gems of the world along a scale from one
to ten. In practice, the softest stone is talc,
with a hardness of one. The hardest stone is diamond, with
a rating of ten. A stone of higher hardness will scratch a
stone of lesser number on the scale. Quartz, with a hardness
of 7, will scratch hematite with a hardness of 4. While you
should not try to perform this test on jewelry set in finished
form, it is a good idea to know relative harnesses to avoid
damaging your inventory.
Quartzes,
agates and jaspers are all relatively hard stones (Moh's 6-7),
but rhodocrosite (hardness 4, second
from right in picture), malachite
(3.5 - 4) and fluorite
(4) are all stones that should be stored and worn with care.
Beyond
these criteria, gemologists may also use density, transparency,
refraction, spectral analysis, and fluorescence to unlock
a stone's identity. For everyday examination, these methods
are beyond the grasp of most of us stone aficionados. We tend
to rely on our experience and "go with the gut"
when making a questionable identification. Often we will find
a customer who knows a particular stone at sight, while just
as often a customer will claim to "know a lot about stones"
only to mispronounce labradorite
or misidentify sodalite
as lapis.
Ultimately
it can be very difficult to identify a stone based on the
small sample set in a pendant or ring. A particular specimen
may not be representational of the rest of its family and
can thus be difficult to classify. What I do is look at the
details of the stone, including its color, grain, inclusional
qualities and its overall character, then try to cross reference
those pieces of the puzzle mentally with what I know about
gemstones from past experience. Obviously the more you know,
the better you will get at identifying those hard to classify
stones.
If I think
they are jasper
or agate,
I will give the identification with the caveat that I am not
100% sure. I know from my own experience with the products
we sell on our site that most unknowns are either agate or
jasper, but this rule may not apply to other vendors' merchandise.
When we
ship out our pendants
or rings
by the gram, one of the best ways to order is as an assortment.
If you definitely need tiger eye or carnelian (for example),
then by all means order by stone. When you order assorted
stones, you will almost always get some unusual and exciting
stone that you have no idea how to identify. As a rule, we
ship these assortments with the following stones:
amethyst,
rose quartz, carnelian, onyx, rainbow moonstone, labradorite,
sodalite, lapis lazuli, snowflake obsidian, amazonite, dendritic
agate, malachite, nephrite jade, chrysocolla, mother of pearl,
abalone, rhodonite, rhodocrosite, tiger eye, fluorite, ruby
zoisite, assorted jaspers and agates.
This is
a partial list. There are many other stones that we get only
a few pieces here and there. If you are having trouble identifying
stones, there are several good resources I can recommend.
Some good websites are: http://www.jewelrymall.com/stones/,
http://mineral.galleries.com/minerals/gemstone/class.htm,
http://www.minerals.net.
A great
book I use all the time is Gemstones of the World by
Walter Schumann. It has over 1500 photos and lots of great
background. You can buy it http://amazon.com.
If you
ever need help identifying a stone or have questions about
something you bought from us, don't hesitate to give us a
call at 888-408-0072 (808-822-2335 international callers),
or drop me an email.
I'll always do me best to answer your question in a timely
manner.
(This
article written by Mike McGinnis and published originally
on indiasilver.com.
We encourage republication but stipulate the piece be copied
in its entirety with links and attribution.)
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