Moldavite

Moldavite
Moldavite from Besednice, Bohemia, Czech Republic
General
Category	Glass
Formula (repeating unit)	SiO2(+Al2O3)
Crystal system	Amorphous
Identification
Color	Mossy green
Mohs scale hardness	5.5
Luster	Vitreous
Diaphaneity	Opaque, translucent, transparent
Specific gravity	2.32 to 2.38
Optical properties	Isotropic
Refractive index	1.48 to 1.54
Birefringence	None
Pleochroism	Absent
Dispersion	None
References

Moldavite (Czech: ) is an olive-green or dull greenish vitreous substance possibly formed by a meteorite impact in southern Germany (Nördlinger Ries), which would make it one kind of tektite. They were introduced to the scientific public for the first time in 1786 as “chrysolites” from Týn nad Vltavou in a lecture by professor Josef Mayer of Prague University, read at a meeting of the Bohemian Scientific Society (Mayer 1788). Zippe (1836) first used the term “moldavite” derived from the town of Moldauthein (Czech: ) - now in Bohemia (the Czech Republic), from where the first described pieces came.

Moldavite's bottle-green glass colour led to its being commonly called Bouteillen-stein, and at one time it was regarded as an artificial product, but this view is opposed to the fact that no remains of glassworks are found in the neighbourhood of its occurrence; moreover, pieces of the substance are widely distributed in Middle to Upper Miocene and younger fluvial clays and gravelly sands in Bohemia and Moravia.

In 1900, F. E. Suess pointed out that the gravel-size moldavites exhibited curious pittings and wrinkles on the surface, which could not be due to the action of water, but resembled the characteristic markings on many meteorites. Boldly attributing the material to a cosmic origin, he regarded moldavites as a special type of meteorite for which he proposed the name of tektite. However, for a long time, it was generally believed to be a variety of obsidian. Because of their difficult fusibility, extremely low water content, and its chemical composition, the current overwhelming consensus among earth scientists is that moldavites were formed about 14.7 million years ago during the impact of a giant meteorite in present-day Nördlinger Ries. Splatters of material that was melted by the impact cooled while they were actually airborne and most fell in Bohemia. Currently, moldavites have been found in an area that includes southern Bohemia, western Moravia, the Cheb Basin (northwest Bohemia), Lusatia (Germany), and Waldviertel (Austria).Isotope analysis of samples of moldavites have shown a beryllium-10 isotope composition similar to the composition of Australasian tektites (australites) and Ivory Coast tektites (ivorites). Their similarity in beryllium-10 isotope composition indicates that moldavites, australites, and ivorites consist of near surface and loosely consolidated terrestrial sediments melted by hypervelocity impacts.