You will need
- - strong magnifier;
- - Refractometer;
- - color filter.
Put the stone on a white sheet of paper and evaluate its color. All the emeralds are colored in different shades of green. If the colouring are yellowish tone, most likely in front of you green garnet or peridot. Green emeralds have a bluish hue.
Under the bright light, turn the stone. Pay attention to variance. Gemologists call this word flashes or sparks of light generated due to the different inclusions. At emeralds the dispersion level is low, so the natural stones give a little "fire". If the gem sparkles and shimmers, most likely, before you cubic Zirconia.
Check the stone on the Refractometer. The refractive index of the emeralds is approximately 1,58.
Green, which is so sought after emeralds, occurs due to the large presence in the composition of the mineral chromium. So the emeralds under the color filter looks brown or red. But the filter does not allow to distinguish natural emerald from synthetic.
Exactly the same shade underneath the filter has a green fluorite, but it is much softer than emerald and is easily scratched even glass. Fluorite under ultraviolet light fluoresces a violet light. At emeralds and luminescence, and fluorescence are rare and usually have red or green.
Carefully inspect the faces of the stone. Very common imitation of emeralds, called "doublet" or "triplet" Is like a sandwich of glass, green epoxy and thin slice of low-quality emerald. When viewed from the side forgery can be clearly seen.
Note the "worn" edges. The Mohs ' hardness of emeralds is quite high, so they remain faceted. Glass imitations quickly wear out. Under a strong magnifying glass is clearly visible.
Natural emeraldx is always present and foreign inclusions. They are clearly visible under a magnifying glass or a microscope. Therefore, the emeralds seem a bit muddy. All these cracks, bubbles and feathers do not damage the minerals. Jewelers call this effect the term "Jardin" (from FR. "the garden"). In-grown stones such defects almost never occur.
Interestingly, some gems-imitation, for example, transparent jade or green garnet-demantoid high quality may have a higher price than a natural emerald of medium quality.
Specify the origin of the stone. The color of Colombian emeralds is due to vanadium, not chromium, so under the color filter, they remain green.