Moldavite — The Green Tektite of the Bohemian Strewnfield
Moldavite — The Green Tektite of the Bohemian Strewnfield
Natural impact-glass formed by the Ries crater event 14.7 million years ago, scattered across what is now the Czech Republic
Moldavite is a bottle-green to forest-green natural glass formed by the impact of a major meteorite at the Ries crater in southern Germany approximately 14.7 million years ago, with the resulting tektite material scattered across a strewnfield extending principally across the territory of the modern Czech Republic. Moldavite is the best-known of the European tektites and one of the most prized varieties of the broader tektite family, with its combination of attractive colour, characteristic surface sculpting, and limited geological extent supporting strong collector and gem-trade demand. The name moldavite derives from the Moldau (Vltava) river of Bohemia, near which much of the original material was collected.
Origin and the Ries impact
Moldavite formed when a meteorite, estimated at approximately 1.5 kilometres in diameter, struck the European landmass at what is now the Nordlinger Ries crater in southern Germany. The impact, dated by radiometric methods to approximately 14.7 million years ago in the middle Miocene epoch, ejected molten silicate material that solidified in flight as droplets and elongated forms before falling back to earth across a strewnfield approximately 450 kilometres east of the impact site. The strewnfield covers principally the regions of southern and western Bohemia in the modern Czech Republic, with smaller distributions in Moravia and Austria.
The Ries crater itself measures approximately 24 kilometres in diameter, and its impact origin was firmly established by the geologist Eugene Shoemaker and colleagues in the 1960s after extensive study of the crater's morphology and the high-pressure shock minerals (coesite, stishovite) found in its rocks. The connection between the Ries crater and the moldavite strewnfield, suspected from the early twentieth century on the basis of geographic proximity and chemical evidence, was confirmed by the radiometric age dating that places both events at the same time in the middle Miocene.
Composition and properties
Moldavite is silica-rich glass — typical compositions are approximately 75 to 80 percent SiO2, with significant aluminium, iron, magnesium, calcium, sodium, and potassium oxides making up the balance. The composition reflects the mixed sedimentary target rocks at the Ries impact site, which were melted and homogenised by the impact-energy heat. The green colour comes principally from divalent and trivalent iron in the glass, with the specific shade varying from light yellow-green through olive to deep forest-green depending on the iron content and the exact thermal history.
Refractive index ranges approximately 1.48 to 1.51, specific gravity 2.32 to 2.38, and Mohs hardness 5.5 to 6. The material is amorphous (non-crystalline) and shows no birefringence under polarised light. Surface sculpting — flow lines, regmaglypts, lechatelierite inclusions, and gas bubbles — is characteristic and provides a useful first-line identification for natural moldavite versus the green bottle-glass imitations that have been produced commercially since the early twentieth century.
Cutting and use
Moldavite is brittle and relatively soft compared with most gem materials, and is typically cut as freeform shapes that preserve the natural surface sculpting on one face, or as faceted gems where the rough is large and clean enough to support the cutting yield. Cut stones are usually under 10 carats; larger pieces are kept as natural specimens for collectors. Faceted moldavite presents the green colour with surprising depth and brilliance for a glass, and well-cut stones are attractive in pendants and earrings.
The material's brittleness and modest hardness make it unsuitable for daily-wear ring use; settings should be protected, and cleaning should be by mild soap and water rather than ultrasonic or steam methods.
Market and imitations
Moldavite has experienced strong price increases since approximately 2010, driven by collector interest in the material's extraterrestrial-impact origin, by the limited geographic extent of the strewnfield, by the closure of significant historical collecting localities under the Czech mining authority, and by a wave of new-age and metaphysical interest that has brought non-traditional buyers into the market. Per-gram prices for fine specimens have risen substantially, and the market for finished moldavite jewellery has grown correspondingly.
Imitations are a real concern. Green bottle glass and various artificially-produced glasses can superficially resemble moldavite at a casual glance, particularly in tumbled or polished form. Genuine moldavite is identified by the characteristic surface sculpting, by lechatelierite (silica-glass) inclusions, by gas bubbles, and by the specific composition revealed by chemical analysis. Buyers should obtain material from reputable specialist dealers with documented provenance from the recognised strewnfield localities. See also: tektite; impact glass.