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The Discovery 1960
Research on the Ries crater or Ries Basin has a rather long tradition. It started as early as 1792 when Carl von Caspers discovered and described a “volcanic tuff” at the Ries (later called suevite) and used it as building material for fortifications although it had been used as building stone already by the Romans. The Ries was geologically mapped as early as 1834 (von Cotta and others, e.g. von Voith, 1835). Detailed geological and petrographic analyses were made by von Gümbel (1870) and many others later on. The name suevite – derived from “suevia”, the Latin name for the teutonic tribe “Schwaben” - was introduced by Sauer (1901) and described in more detail by Sauer (1920) and Schnell (1925). Oberdorfer, (1905), Löffler (1912) and others were the first to recognize unusual deformation and transformation effects in mineral phases of crystalline rock clasts in suevite and might actually have seen coesite but didn’t recognize it.
The Ries Basin was interpreted by most workers as a volcanic phenomenon, an interpretation which was kept alive until July 1960 when Eugene M. Shoemaker from the US Geological Survey came to the Ries and sampled suevite at the quarry of Otting. He sent the sample back to his USGS colleague Edward C. T. Chao who discovered the high pressure modification of quartz named coesite by X-ray diffraction analysis. This mineral had been discovered shortly before at the Arizona crater (Barringer crater) whose origin by impact of an iron “meteorite” was beyond any doubts. The revolutionary discovery of coesite in the Ries suevite was published by Shoemaker and Chao in 1961 and changed the interpretation of the Ries from volcanic to hypervelocity impact from one day to the other. Shortly after this discovery Chao and Littler (1963) detected an even denser high pressure modification of quartz in the suevite of the Ries named stishovite.
Microscopic view of a very highly shocked granitic clast from the Ries suevite with coesite inside diaplectic quartz glass and vesiculated alkali feldspar glass.
