Engineering geology
Suevite

Suevite

Suevite is a shock-metamorphosed rock. It is an impact breccia composed of impact melt and lithic fragments. Impact metamorphism is caused by a collision between Earth and large extraterrestrial body which is usually meteorite or asteroid

According to the IUGS Subcommission, suevite or SueviteBreccia is a polymict impact breccia with clastic matrix and mineral clasts in various stages of shock metamorphism including cogenetic impact melt particles which are in a glassy or crystallized state.

Originally, suevite was the name of a melt breccia in the Ries crater and derived from the province of Swabia in southern Germany, and such means “Swabian stone”. For decades, the Ries crater suevite was considered a peculiar volcanic breccia and unique in the world. Both the volcanic origin and the uniqueness had to be abandoned when the Ries suevite was shown to be a strongly shocked impactite and comparable rocks were found in many other impact structures worldwide.

ries crater, suevite, cat face, Aumühle quarry
Cut face of a Ries crater suevite from the Aumühle quarry. The larger pale clasts are all fragments from the crystalline basement. Some flow texture adjusting clasts can be observed.

Significant debate has ensued as a consequence of two publications promoting the idea that suevite from the Ries crater, for 50 years considered a melt-fragment-bearing impactite with an essentially clastic matrix (“particulate matrix” according to, should rather be considered impact melt rock with a melt groundmass. This idea questions the validity of the term “suevite” (and by implication) the entire polymict-impact-breccia nomenclature of the IUGS subcommission.

ries crater, suevite, Aumühle variety, gneiss cobble in suevite
Ries crater: a partly melted gneiss fragment in a suevite-breccia from the Aumühle quarry. Higher impact shock levels may lead to complete melting and glass formation. As larger particles embedded in the breccia they are called “flat cakes”
Close up of the gneiss fragment from Fig. above; Partially the crystalline rock is melted to a vesicular glass. Shock pressures for total-rock melt must exceed roughly 60 GPa (600 kbar).

Source: impact-structures;sandatlas

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