Identifying Gemstones

By Solomon Onwude


In gemstone identification, you have to first of all ask your self: to what extent you intend going on this (gemstone collection).

Now, there are two kinds of gem identification tasks: determinative and confirmative.

Determinative ID is when someone hands you a rough piece of rock and asks what it is.
Confirmative identification is when someone wants to sell you a stone - usually already cut - and you want to confirm that the gem is as advertised.

Determinative identification skills may take many years to develop, and may involve the use of an array of expensive equipment for measuring everything from density to various optical properties or even thermal conductance.

Confirmative identification of gems is much easier to learn and may often be accomplished without any tools at all other than your eyes.

Gemology has been defined as the "scientific study of gemstones" There may be investors whose only interest is in the value of the stones, but if they ever need to distinguish one gem from another, they are dealing with science. It is nearly almost impossible to remove science from gemstone identification!

There are several different categories of gemologist - jewelers, goldsmiths, lapidary, faceters, gem scientist. All these people identify gemstones for various reasons and they use several different techniques in order to achieve this.

Some simple tests that could help you identify gemstones include: Scratch tests, where the unknown is scratched by various substances, will determine its hardness. Other useful tests are the reaction to acids and the flame of a blow torch. These are categorized as destructive tests and are obviously inappropriate for cut gems.

It has been said and written that: For centuries it was the lapidary who was in a position to most easily recognize the differences in like appearing gems. During the cutting process gems get viewed intently, a perspective that no other gemologist has. Identifying inclusions are given a lot of attention, then as many as possible removed. Differences in hardness are readily apparent when cutting and polishing, as are other characteristics.

... A method needed to be devised where cut gems could be identified without damage. To this end scientists began to first, identify the measurable physical and optical properties of our gems. Next they devised instruments to measure these properties. There was a long process of systematically measuring and recording these properties so they could be looked up. (Though well established, this is actually an ongoing process.) Eventually all this got put together into methods that could be used by people without extensive scientific backgrounds or large and expensive laboratory equipment.

... That is not to say that it doesn't require substantial education to identify gems. It is a large and complex subject that is continuing to increase in complexity as new gems are discovered and new ones are created in the laboratory. However, one doesn't need a degree in chemistry or physics to simply measure the properties of our gems. The most esoteric part was discovering those properties and creating the tools to measure them.

Finally, I would like to share a simple method of gem identification with you: "the Hodgkinson method of gem identification" - Its the dirty version though - after Alan Hodgkinson. All you need are your eyes and some clean hands. Pick up a stone in question and hold it up very close to your eye so that you can look into the table. You must hold it very close without touching - almost like inserting a contact lens, but again not touching. Look literally through the stone at a distant source of light such as a lamp or light bulb. You will see a number of reflections of the distant light source as they bounce around within the stone.

Roll the stone around its axis and tilt it slightly while watching the reflections. Due to the refractive properties of gemstones, each reflection will to some extent appear as a small rainbow. This is a single one of those rainbows as it appears looking through a spinel at the filament of a clear light bulb about 6 feet away:

Depending on the gem material in question, that rainbow will have varying properties. If the gem is doubly refractive you are likely to see doubled or ghosted (rainbow) images. Because the gem may be cut in any orientation with respect to the crystal structure (which is responsible for these phenomenon) you may have to examine the stone from a variety of angles to be sure whether it is doubly refractive OR NOT.

Hope you find some of these exciting and not boring...

Cheers

Solomon
Global Roughs Inc
http://www.globalroughs.com

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