Gemstone Identification: How to Identify Gemstones at Home

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Introduction

So, you've bought some loose gemstones, and now you want to know what kinds you have. Many people ask, "How to identify this gemstone?" "What kind of stone is this?" or "How to test gemstones at home?" With a bit of practice, some gem tools, and this guide, you'll be able to identify different gemstones like topaz and tourmaline in just a few steps. If you enjoy solving puzzles, you'll find this process fun!

As you follow the steps and train your eye, you'll start to recognize that red garnets, for example, don't look like Burma rubies or red andesine. With practice, you'll become really good at identifying stones just by looking at them. All you need is a good reference book, some basic gem tools, and a bit of practice.

Before you start, clean your stone with a gem cloth. Fold the cloth into a square, then tuck your stone in the cloth and rub it between your fingers to remove any dirt, fingerprints, or dust. Keeping your stone clean is important, so use tweezers to hold it whenever you can to keep it clean throughout the process.

Using Gemstone Identification Charts

Get a gemstone identification chart. If you plan to identify gemstones often, it's a good idea to buy a printed chart or reference book. Look for ones endorsed by the Gemological Institute of America (GIA) or the American Gemological Association.

If you only need to identify gemstones occasionally, you can find basic gemstone identification charts online. They may not be as detailed, but they can help in a pinch.

The Hiddenite Gems chart is useful if you know the color and hardness of the gemstone.
The Gem Select RI chart helps if you know the refractive index and birefringence.
The American Federation of Mineralogical Societies (AFMS) offers a free Mohs Scale chart.

Basic Observation: Color, Transparency & Specific Gravity

Tools Needed: Tweezers, 10x loupe, Light source

Start by looking at the gemstone with your eyes or a 10x loupe in good light, like daylight or a strong lamp. You don't need a microscope at this stage. Hold the stone about a foot away from your eyes, on a white or gray background (like a gem cloth), and observe it both face-up and from the side under bright light.

Color: Hue, Tone, Saturation

Hue: This is the basic color of the gemstone. For example, is it blue or a bit greenish blue? Try to be as specific as you can. There are 31 colors in GIA's color wheel, so the more precise you are, the easier it will be to identify the stone later.
Tone: This describes how light or dark the color is. Determine if the color is light, medium, dark, or somewhere in between. GIA uses seven levels, from very light to very dark.
Saturation: This measures the strength of the color. Is it dull, strong, or vivid? For warm colors (yellows, oranges, reds), check for brownness; less brown means higher saturation. For cool colors (blues, greens), look for grayness; less gray means higher saturation. If you don't see any brown or gray, the color is likely strong.

Transparency and Specific Gravity

Transparency: Determine if your gemstone is transparent (see-through), translucent (partially see-through), or opaque (not see-through). Also, check how much "fire" or sparkle it has and note if it's strong, moderate, or weak.
Specific Gravity: Gently bounce the stone in your hand to feel its weight. Does it feel as heavy as it should for its size, or is it heavier or lighter than expected? This gives you a rough idea of the stone's specific gravity.

Light It & Loupe It: Optical Effects and Luster

Tools Needed: Tweezers, Penlight, 10x loupe

Optical Effects: Shine a penlight or any focused, bright light across the stone to see if it shows special effects like color changes, star patterns, cat's-eye effects, floating shimmer, or sparkle.
Luster: Rotate the stone so light reflects off its surface, and examine it both with your eyes and with a 10x loupe. What does it look like? Is it shiny, dull, waxy, metallic like a diamond, glassy, greasy, or silky?

If there are any chips on the stone, check the surface inside the chips. Is it smooth like seashell rings, straight like steps, gritty, splintery, or uneven? Also, note the luster in these chipped areas.

Measuring Refractive Index and Birefringence

Tools Needed: Refractometer & Refractive index (RI) fluid

Refractive Index (RI): Measuring the RI of a gemstone is very helpful for identifying it. The best way to get an accurate RI is by using a refractometer, but it can take some practice.
Prepare Your Tools: Ensure your stone is clean. If your refractometer doesn't have a built-in light, shine a light into its light port. Monochromatic light (one color) is clearer than white light. Keep the refractometer's cover closed to avoid interference from ambient light, and regularly check its calibration with a known stone.
Apply RI Fluid: Place a small drop of RI fluid on the metal surface of refractometer. This fluid helps to connect the stone to the refractometer. Use only a small amount.
Place the Stone: For a faceted or cabochon stone, put the best-polished side down on the fluid drop and gently slide it to the center of the refractometer. Align long stones (like marquise or oval) lengthwise with the crystal. For freeform stones, touch the polished surface to the fluid and crystal. Only polished stones will give a reading; rough stones won't.
Adjust Fluid: If the stone seems to float or you see rainbow colors, use a tissue to remove some RI fluid. If the image looks scattered or the stone doesn't move smoothly, add more fluid.
Take the Reading: Look through the viewer lens (without magnification) and move your head slowly up and down. You'll see a "bubble" outline—this is your RI reading. Note the bottom of the bubble's outline to the nearest hundredth (0.01). Then, use the magnifying lens for a more precise reading to the nearest thousandth (0.001). Keep the stone on the crystal for birefringence testing.
Head Bobbing Tip: Moving your head slowly helps reveal the bubble. If you focus too hard, it might be harder to see. The reading might not be exact, but with practice, you'll get a close enough result. RI values often come in a range due to variations from different mines, so don't worry if your reading isn't perfect. You can always retry if needed.

Birefringence Testing

Birefringence testing helps you learn more about your gemstone. Here's how to do it:

Turn the Stone: While the stone is on the refractometer, rotate it about six times, making each turn roughly 30 degrees until it has turned 180 degrees (upside down).
Follow a Clockwise Pattern: Imagine the stone is a clock with 12 at the top & 6 at the bottom. Start by turning the stone so the top edge moves to about 1 o'clock, and take an RI reading. Continue turning the stone to 2 o'clock, 3 o'clock (which is halfway), 4 o'clock, 5 o'clock, and finally to 6 o'clock. Record the RI reading at each position on a piece of paper. If the readings don't change, do at least three turns to be sure. Calculate the birefringence by subtracting the lowest reading from the highest and rounding to three decimal places (0.001).
If the Fluid Dries: The RI fluid might dry up during the test. If the readings start to look unclear, clean off the stone and the refractometer, add a new drop of RI fluid, and continue testing.
Refractometer Care Tip: If you're not using the refractometer for a while, rub a small amount of petroleum jelly on the hemicylinder to stop tarnishing.
Over The Limits (OTL): The RI fluid has a reading of 1.80. Stones with an RI above this (like diamond and zircon) won't show a reading on the refractometer. Similarly, stones with an RI below about 1.35 (like fluorite and opal) will also be hard to measure.

Testing for Single vs. Double Refraction

Tools Needed: Polariscope

A polariscope helps you figure out if your gem is singly refractive (SR), doubly refractive (DR), or an aggregate (AGG). Note: Only use a polariscope with transparent or translucent gemstones, as opaque ones won't give a clear reading.

How to Use:

Turn on the Light: Place your gem face down on the lower glass lens of the polariscope (the polarizer).
Look Through the Analyzer: Look down through the top lens (the analyzer) and turn it until the area around the gemstone looks the darkest. This is your starting point.
Rotate the Analyzer: Slowly rotate the analyzer 360 degrees, watching the area around the stone change from light to dark and back to light. This helps you identify the refraction type.

Tips:

Trouble Seeing Changes? If it's hard to see the light/dark change, try covering the analyzer with a white card with a small hole to reduce distractions. Look through the hole for a clearer view.
If the Stone Remains Dark: It's likely singly refractive (SR). Rotate the stone and check from different angles to confirm. If it stays dark from all views, it's SR.
If the Stone Remains Light: It's probably an aggregate (AGG). Sometimes, a doubly refractive (DR) stone might appear as AGG due to inclusions or high RI. If the stone "blinks" between light and dark, it might be DR or have anomalous DR (ADR). Stones with ADR include amber, opal, synthetic spinel, and some garnets. Look for a "crosshatch" pattern for ADR.

Additional Tips:

High RI Stones: Test these on their sides instead of face down to reduce light interference.
Small Stones: Use the magnifying lens from your refractometer on top of the analyzer lens for a better view.
Red Stones: If the RI is 1.73 or higher, skip the polariscope and use a dichroscope instead.

Conclusion

You've likely gathered enough information to identify your gemstone. Look up the gemstones that match your stone's color and refractive index (RI). Often, this information alone is enough to determine the exact type of gem. In fact, you can identify 95% of gemstones with this simple test since each gemstone has a unique RI.

If you still have more than one possibility, use birefringence and the single vs. double refraction tests to narrow it down further. Only a few gemstones will remain unidentified after these tests, and those may need more advanced analysis to determine their exact type.