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The agate occurrences of Schweighausen were probably already used in the Middle Ages by the gemstone-cutteries in Freiburg and Waldkirch. The agates were looked for in the loose slope debris of the Geisberg, at the hay place, on the Weißmoos, at the Lindenrain and to Hühnersedel. In the modern times a quarry at the Geisberg was operated, in which nowadays however no finds are more possible. The original agate occurrences lie in a characteristically red dyed, very vesicle-rich porphyric layer. The nodules achieve partially enormous sizes to about 40 cm diameters, however they often contain a big part of porous and unaesthetic material, so that only the upper, substantially smaller part can be used for polishing.



Above the red porphyric layer lithophysae (thundereggs) occur in a white layer  of porphyric ashes. These are usually red and carnelian-alike. Blue, yellow and red-violet tones occur more rarely.