how to identify genuine moldavite is "Moldavites: Natural or Fake?" authored by Jaroslav Hyrsl and published in the Spring 2015 issue of Gems and Gemology.
Fortunately, the identification of faceted moldavite is simple. Besides their flow texture and abundant bubbles (almost always much more abundant than in an artificial glass), moldavites contain “wires” of lechatelierite, a high-temperature form of SiO2. Lechatelierite is very easy to see with a loupe due to its lower RI.
Propertis
-Color: Brownish black, grayish black, dan Black (Tektite) & brownish green, grayish green, dan green (Moldavite).
-Chemical composition: SiO2(+AI2O3) silicon dioxide + (aluminum oxide)
-Transparency: Transparent to opaque
-Refractive index: 1.48 – 1.51 +/-
-Double refraction: None
-Crystal system: Amorphous
-Dispersion: None
-Moh’s Hardness: 5.5 – 6
-Density: 2.32-2.38
-Absorption spectrum: None
-Fracture: Conchoidal
-Synthetic: None
-Imitation: Glass, etc
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The moldavites are usually olive-green in color and clear as a crystal. The deposits in other strewn field near Brno contain darker and leafy green shades, with the tints of brown, yellowish green, green, or greenish brown in color. It has been cut into faceted and cabochon gemstones since the mid-1800s. These are used in rings, earrings, necklaces, pins and other types of jewelry.
The difference between “imitation” and “fake” is in the disclosure. “Imitations” are sold as such. “Fakes” are sold without disclosure.
If you are offered a faceted moldavite over two carats or any moldavite without eye-visible bubbles, there is a good chance that it is fake.
Natural Moldavites typical has bubbles and inclusions of lechatelierite. An almost identical feature can be created artificially, therefore the presence or lack of lechatelierite “wires” is the best diagnostic tool.
(Hobart M. King, Ph.D., GIA Graduate Gemologist)
Source : GIA Gemologist Articles
