Summary
This guide gives you a clear gem identification methodology you can use with any gemstone. You move from visual checks to optical tools, structural tests, and density clues. Each step adds direction, supports your judgement, and leads you to a confident identity.
Introduction
You follow a gem identification methodology to achieve consistent results. To begin, you use your eyes. Then you move to tools that show structure, light behavior, and density. As a result, you follow a gem identification methodology to achieve consistent results.
For example, many buyers feel confused when gemstones look alike. Even so, this method gives you order. More importantly, you can use it in a shop, a field visit, or a classroom. You can also read my guide on Basic Gem Testing Tools for a deeper look at the instruments you will use during this process.
Why This Gem Identification Methodology Matters to You
You follow one clear path. After that, you compare clues from different tests. In the same way, you combine them into one answer. Most importantly, this keeps you from relying on color alone. It also helps you spot gemstones that imitate popular gemstones.
Basic Observation in a Gem Identification Methodology
Your eyes tell you more than any tool. At the same time, each visual clue narrows the field. For instance, cabochons may show stars or cat’s eyes. In contrast, faceted stones reveal dispersion better. Begin with:
Color Clues Used in Gem Identification
Check if the gemstone is colored or colorless. Ruby shows red. Meanwhile, peridot shows green.
Transparency Clues in the Identification Method
Check if the gemstones are transparent, translucent, or opaque. Even then, you still need more tests.
Cut Features in the Identification Process
Check how the gemstone is cut. Cabochons may show stars or cat’s eyes. On the other hand, faceted stones highlight brilliance.
Optical Phenomenon You Note During Identification
Move the gemstone. You may see asterism (star-like features), chatoyancy (cat’s eye-like features), or a color change. Afterwards, you decide which tools to use next.
Luster Clues in Gem Identification
Luster is related to the quality of polish and refractive index. Gemstones with a high refractive index will show higher luster. Glassy for quartz. Silky for fibrous stones. In short, luster supports your early judgment.
Dispersion Signs You Observe in the Methodology
Dispersion is the ability of the gemstone to split white light into its component spectral colors. Dispersion is mostly visible in colorless gemstones. Diamond shows strong fire. Synthetic cubic zirconia (CZ) shows even stronger fire. Therefore, dispersion alone cannot confirm identity.
At this point, you know which tools to use next.
Steps You Follow in a Gem Identification Methodology
You now move from simple checks to measured clues. Similarly, each step supports the previous one.
Polariscope
Single Refractive (SR) Clues Used in Gem Identification
Gemstones stay dark in all positions on a polariscope. Some gemstones may show anomalous double refraction. Diamond, natural spinel, and garnet are good examples. In contrast, beryl and tourmaline are DR.
Anomalous Double Refractive (ADR) Clues in the Identification Method
Some single refractive (SR) gemstones may show light (internal) strain. Synthetic spinel is a good example.
Double Refractive (DR) Features in the Identification Process
Gemstones blink as it is rotated on a polariscope. Beryl, tourmaline, corundum, quartz are good examples.
Aggregate (AGG) You Note During Identification
Gemstones stay light in all positions on a polariscope. Chalcedony, jadeite, nephrite are good examples.
See more examples at the GIA Gem Encyclopedia.
Interference Figure
Uniaxial Cross
Uniaxial gemstones may show two types of figures. They are seen in corundum, quartz, and calcite.
Bull’s Eye
The only gemstones that show the bull’s eye uniaxial figure are some quartzes—a centered uniaxial pattern.
Biaxial Single or Double
Biaxial figures are usually much smaller and more difficult to resolve. Normally, with cut gemstones, only a single type of biaxial figure is seen. The double optic axis type is usually seen only in very thin pieces, which are strongly positive or negative in optic sign. Tourmaline, tanzanite, topaz, and feldspar are good examples.
Refractive Index
To clarify, this is one of your strongest tests. In addition, spot readings help with mounted stones. As a result, you confirm or reject early guesses.
Single Refractive Clues Used in Gem Identification
Faceted gemstones will show one shadow edge on the refractometer table when carefully and progressively rotated through at least 180 degrees. Spinel reads around 1.72.
Double Refractive Clues in the Identification Method
Faceted gemstones will show two shadow edges on the refractometer table when carefully and progressively rotated through at least 180 degrees. Emerald reads 1.565–1.602.
Spot Reading Features in the Identification Process
The distant vision technique provides an approximate refractive index (RI) reading and is particularly used for gemstones with curved surfaces such as cabochons. Useful in mounted stones.
Birefringence You Note During Identification
Birefringence is defined as the maximum amount of double refraction and is determined by subtracting the lowest refractive index (RI) reading from the maximum refractive index (RI) reading. High in calcite. Low in quartz.
Uniaxial (+/–) Clues in Gem Identification
One shadow edge moves on the refractometer table. If the maximum refractive index (RI) ray moves, the gemstone is uniaxial positive. Quarts, zircon are good examples. If the minimum refractive index (RI) ray moves, the gemstone is uniaxial negative. Beryl, corundum, and tourmaline are good examples.
Biaxial (+/–) Clues in Gem Identification
In biaxial gemstones both shadow edges move. If beta is closer to alpha than gamma, the gemstones are biaxial positive. Topaz, peridot, zoisite, chrysoberyl, and spodumene are good examples. If beta is closer to gamma than alpha, the gemstones are biaxial negative. Iolite, feldspar, sinhalite, andalusite are good examples.
You can explore full RI charts at GemSelect or Scribd.
Microscope
You now look inside the gemstone. At this stage, internal features confirm earlier clues. For instance, join lines expose doublets and triplets. Similarly, typical zoning exposes possible synthetic growth.
Assembled Stones Clues in the Identification Method
Doublets and triplets show join lines.
Fractures You Note During Identification
Feathers, fingerprints, stress marks.
Doubling Features in the Identification Process
Visible in many DR (double refractive) gemstones.
Inclusions Features in the Identification Process
Inclusion is a general term used for any defect or irregularity within a gemstone. Liquid, gas, or crystals. Three-phase inclusions support natural Colombian emerald.
Other Signs You Observe in the Methodology
Color zoning and twinning are both examples of growth phenomena.
See more examples in my Gem Inclusions Reference Guide.
Spectrum
Description
In the spectroscope, the wavelengths that have been absorbed by the gemstone appear as a series of dark lines or bands along the spectrum. This series of lines and bands creates a pattern called an absorption spectrum that is distinct to some species of gemstone and can be a valuable means of identifying the gemstone. You see which wavelengths are absorbed. For proper viewing of gemstone spectrum, a concentrated light source is required, and a pocket torch with a focused beam. For example, iron shapes the peridot spectrum. Likewise, chromium shapes ruby.
Pleochroism
Dichroic Clues in the Identification Method
Pleochroism can only be seen in colored double refractive gemstones. Uniaxial gemstones may produce two different colored rays or two rays showing different shades of color. Corundum and tourmaline are good examples.
Trichroic Clues in the Identification Method
Biaxial gemstones may show three differently colored rays. Tanzanite and iolite are good examples.
Colors Seen in the Identification Process
Even so, record both or all tones.
Specific Gravity
Hydrostatic Weighing Clues Used in Gem Identification
Use water and a modern hydrostatic weighing scale. Gemstones should be clean and free from grease. Porous gemstones such as turquoise, some opals, and assembled gemstones may cause problems, in which case you must use other identification procedures. One cannot achieve consistent or reliable results with gemstones smaller than 1.00 carat.
Heavy Liquids Clues in the Identification Method
Of all the heavy liquids, methylene iodide (3.32) is undoubtedly the most useful. Upon exposure to light, methylene iodide has a tendency to turn brown or black, but if a small piece of copper is kept in the bottle, this darkening process can be reversed. After that, compare float-or-sink results in heavy liquids.
Consequently, SG separates most colored gemstones.
UV Fluorescence
Long Wave Clues in Gem Identification
The long-wave radiation sources are medium-pressure mercury lamps. These lamps emit spectral wavelengths down to ultraviolet wavelengths. Ruby glows red.
Short Wave Clues in Gem Identification
Use low-pressure vapor-type mercury lamps as a short-wave radiation source. Short-wave radiation is damaging to human tissue. It is the energy in sunlight that produces sunburn, and by looking directly into a short-wave energy source, much damage can be done to the eyes. For this reason, never look into either long-wave or short-wave lamps to see if they have been switched on or off. Instead, place a piece of white paper under the lamp and observe the effect of the light on the paper. If the paper glows blue white, the light source is switched on; if not, it is switched off. Observe the crown, pavilion, and girdle of the gemstone, as it may be a doublet or triplet. Some diamonds glow blue. Still, UV is a support test, not a final answer.
Phosphorescence
Some diamonds and synthetics glow even after light is removed or switched off. In addition, this helps you separate certain types of synthetics. Phosphorescence is of much lesser importance in gemology.
Chelsea Filter
The Chelsea color filter is useful in indicating the presence of chrome or cobalt in certain gemstones. This helps you spot chromium. For instance, ruby often shows red, while synthetic blue spinel may show orange or red. The Chelsea Filter is not a conclusive test.
Read-Through
Place printed text under the gemstone. The read-through test is a simple method, primarily for diamonds, that checks a gemstone’s light-bending properties.
Immersion Cell
Liquid with a close refractive index (RI) helps you see zoning and assembled gemstones. Therefore, it exposes assembled gemstones clearly.
Magnet
Some iron-rich garnets respond. Meanwhile, most gemstones show no reaction.
Streak
Useful for opaque materials like hematite. However, streak is rarely used for transparent gemstones.
Final Identity You Reach Through a Gem Identification Methodology
Finally, you combine all clues from this gem identification methodology. Most importantly, you confirm species and variety. After that, you identify natural, synthetic, or assembled. If synthetic, you name the process such as flame fusion, flux or hydrothermal. If the trade uses a known name, you add it.
In the end, you reach a confident answer because you follow one system.
FAQ on Gem Identification Methodology
What is the quickest first test?
Visual observation. Still, you must follow up with RI or SG.
Can color alone identify a gem?
No. Therefore, you need supportive clues.
Why does birefringence matter?
Because it separates gemstones with similar RI readings. In addition, it exposes double refraction behavior.
Should you trust UV alone?
No. Instead, treat UV as a support test.
