Moldavite is a tektite — a natural glass formed when a meteorite impact melted and splashed terrestrial rock, in this case about 15 million years ago in what is now southern Germany, scattering droplets that fell across Bohemia and Moravia. It is green, translucent, sculptured by millions of years of etching in the soil, and available only from a small region in limited quantities. Prices have risen sharply, and the market has been flooded with fakes.
The difficulty is that moldavite is glass. The refractometer, polariscope and specific gravity — the tests that expose glass imitating quartz — say "glass" for genuine moldavite too. Separation depends on other features.
What moldavite is
Natural silica-rich glass. Properties: RI about 1.48–1.50 (one reading), SG 2.32–2.38, hardness 5.5–6, singly refractive with some strain, colour olive to bottle green, translucent, and — critically — a specific set of internal and surface features.
Genuine features
Surface sculpture. Natural moldavite has been etched by groundwater for millions of years into a surface of pits, grooves, ridges and wrinkles that is irregular, deep, and varies across the piece. The sculpture on high-quality pieces is intricate and follows flow structure in the glass. Fakes are moulded with a "sculpture" that is shallow, repetitive, and identical from piece to piece.
Lechatelierite. Wormy, wispy inclusions of pure silica glass — from quartz grains that melted incompletely — with a distinctive contorted shape and a slightly different RI from the host, visible under magnification. Very characteristic of tektites and absent from manufactured glass.
Flow structure. Swirled, folded layering of slightly different composition, visible as schlieren in transmitted light, with the lechatelierite drawn out along it.
Bubbles. Present in genuine moldavite, usually elongated or flattened along the flow, sometimes in quantity, sometimes almost absent. Manufactured glass tends to have round bubbles.
Colour. Muted olive to bottle green, sometimes brownish. Bright, uniform, emerald or grass green is suspicious.
Fake moldavite
Moulded bottle glass. Green glass cast in moulds taken from real pieces or designed to look sculptured. Repetitive surface; round bubbles; no lechatelierite; often too bright or too uniform in colour; sometimes with a glossy, un-etched look in the recesses where genuine moldavite is matte; mould seams.
Faceted "moldavite". Genuine moldavite is faceted in small quantities; much faceted green "moldavite" is bottle glass. The internal features decide.
Slag and industrial glass. Occasionally passed off as tektite.
How the laboratory examines it
Confirms glass by RI and polariscope (so far the same as a fake). Then magnification: lechatelierite, flow structure, bubble shape. Surface examination: depth, irregularity and matte texture of the sculpture versus moulded repetition. Comparison with reference material. Report states: natural tektite (moldavite) or manufactured glass, with the features on which the conclusion rests.
Note that some fakes are good enough that a laboratory may report characteristics consistent with natural tektite rather than a flat certainty, and that honesty is preferable to false confidence.
Frequently asked questions
Does moldavite scratch glass?
Moldavite is glass with hardness 5.5–6, about the same as ordinary glass. The scratch test is useless here.
Is moldavite radioactive or magnetic?
No. Neither property helps identification.
Why does my moldavite have bubbles?
Genuine moldavite commonly contains bubbles, often flattened. Bubbles alone neither confirm nor condemn; their shape and the presence of lechatelierite matter.
Can moldavite be tested cheaply?
Identification is a magnification examination and is inexpensive relative to current moldavite prices, where even small pieces carry significant cost.
Are all pieces from the Czech Republic?
Essentially yes — moldavite is defined by its strewn field in Bohemia and Moravia. "Moldavite" from anywhere else is either mislabelled tektite of another type or glass.