When in doubt, look for a book or chart endorsed by the Gemological Institute of America (GIA) or the American Gemological Association.
The Hiddenite Gems’ gemstone identification chart can be used when you know color and hardness. The Gem Select RI chart can be used when you know refractive index and birefringence: http://www. gemselect. com/gem-info/refractive-index. php The American Federation of Mineralogical Societies (AFMS) offers a free Mohs’ Scale chart: http://www. amfed. org/t_mohs. htm
True gemstones have a crystalline structure. This structure can be shaped through cutting, fracturing, and abrasion, but it has fixed planes that cannot be altered by pressure alone. [1] X Research source Don’t hit a stone with a hammer if you don’t want to shatter it. Real gemstones don’t get bent or reshaped, but they do break.
Synthetic stones often have curved growth patterns inside the stone rather than angular growth patterns. [3] X Research source Gas bubbles that are round and come in large strings are often an indication, but be careful, since a gas bubble in an inclusion can occur within natural stones. Platinum or gold platelets can stick to synthetic stones. Fingerprint-patterned inclusions are common in synthetics, as are nail-shaped inclusions, chevron (v-shaped) growth patterns, wispy veil-like inclusions, and interior columnar structures.
The surface of an imitation may look pitted and uneven, like an orange peel. Some imitations have swirl marks known as “flow lines. " Large, round gas bubbles are common within imitations. [5] X Research source Imitations tend to feel lighter than their natural counterparts.
Use a penlight to illuminate the stone when checking for signs of assembly. Look for differences in luster or for colored and colorless cement. Also look for the “red ring effect. " Turn the stone face down and look for a red ring along the outer part of the stone. If you spot the red ring, you probably have an assembled stone.
Do not shine a light into the stone to examine its color unless you have a dark stone and need to determine whether it is black, dark blue, or another deep color. “Hue” refers to the stone’s overall body color. Be as specific as possible. For instance, if a stone is a yellowish green, identify it as such instead of merely saying “red. " The GIA separates stone hue into 31 different colors. “Tone” refers to whether a color is dark, medium, light, or somewhere in between. “Saturation” refers to the intensity of color. Determine whether the hue is warm (yellow, orange, red) or cool (purple, blue, green). With warm colors, check the stone for brown tints. For cool colors, check the stone for gray tints. The more brown or gray you see, the less saturated the stone color is.
Transparent stones are completely see-through (example: diamonds). Translucent stones can be seen through, but some color or haze alters the image (example: amethyst or aquamarine). Opaque stones cannot be seen through (example: opal).
To judge heft, bounce the stone in the palm of your hand and ask yourself if it feels as heavy as you would expect for its size or if it feels heavier or unusually light. Specific gravity readings are fairly outdated as a practice among gemologists, and heft measurements are used as a relatively accurate estimation. For example, aquamarine has low heft while blue topaz, which is similar in appearance, has a high or heavy heft. Similarly, diamond has a lower heft than synthetic cubic zirconia. [9] X Research source
The most common cut styles you will run across include faceted, cabochon, cameo, bead, and tumbled. Within each of these basic cut styles, you will usually see sub-styles, as well.
Some stones are physically harder than others, and hardness is usually measured by the Mohs’ Scale. Use the various substances provided in a hardness kit to scratch the surface of the gemstone. If the stone can be scratched, it is softer than the substance you scratched it with. If the stone cannot be scratched, it is harder than the substance. To test streak, drag the stone across a ceramic plate. Compare the streak left behind to the streaks illustrated on a streak chart. [10] X Research source “Cleavage” refers to the way a crystal breaks. If there are chips along to surface, examine the area inside the chips. If not, you will need to strike the gemstone hard enough to break it. Ask yourself if the area is rounded like rings on a seashell (conchoidal), straight like steps, granular, splintery, or uneven.
Check for optical phenomena by passing a pen light across the stone’s surface. Color change is one of the most important optical phenomena to look for, and every stone should be checked for color change. Look for changes in color between natural light, incandescent light, and fluorescent light. [11] X Research source
To check for luster, turn the stone, allowing light to reflect off its surface. View the stone with the naked eye and with a 10x loupe. Determine if the stone looks dull, waxy, metallic, shiny (adamantine), glass-like (vitreous), greasy, or silky.
Shine a penlight through the stone and examine the fire inside the stone. Ask yourself if the fire is weak, moderate, strong, or extreme. [12] X Research source
Place a small bead of RI fluid on the metal surface of the refractometer near the back of the crystal hemicylinder (the window on which the stone will sit). Place the stone facet face down on the fluid dot and slide it toward the middle of the hemicylinder crystal using your fingers. Look through the viewer lens without magnification. Continue looking until you see the outline of a bubble, then look at the bottom of this bubble. Take the reading from there, rounding the decimal to the nearest hundredth. Use the magnifying lens to take a more specific reading and round it to the nearest thousandth.
Perform a standard RI test. Instead of keeping the stone still, gradually turn it 180 degrees, making each separate turn about 30 degrees. At each 30 degree mark, take a new RI reading. Subtract the lowest reading from the highest to find the stone’s birefringence. Round it to the nearest thousandth.
Turn on the light of a polariscope and place the stone face down on the lower glass lens (polarizer). Look through the top lens (analyzer), turning the top lens until the area around the stone looks darkest. This is your starting point. Turn the analyzer 360 degrees and watch how the light around the stone changes. If the stone appeared dark and stays dark, it is likely an SR. If the stone starts light and stays light, it is likely AGG. If the lightness or darkness of the stone changes, it is likely DR.
