Porcelain
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Porcelainite is a white rock , dark blue or gray due to impurities, which has a low level of metamorphism and which emerges from the original rock through silicification . It forms under increased pressure and temperature conditions in the border area of diagenesis from opal , which is formed in sediments of the deep sea . The silicic acid of the opal comes from the tiny skeletons of radiolarians , diatoms , sponge needles or similar marine life with a pebble skeleton, more rarely from volcanic silica. The opal of porcelain is available in low-temperature modifications of cristobalite and tridymite . In the further course of the diagenesis, porcelainite turns into quartz, so that the rock is then referred to as quartz chert . The conversion of porcelain to quartz chert is not only dependent on pressure and temperature, but also a function of time. In the North Atlantic, therefore, the oldest known porcelainites are from the Lower Cretaceous .
Porcelainite also occurs in lake sediments, where they can develop from diatomaceous earth under suitable conditions . For example, they can be found in the rocks of the Rott fossil deposit near Bonn.
Stone axes were made from porcelain in Ireland in the Neolithic . Tievebulliagh and Rathlin Island ( County Antrim ) have been identified as mining sites . The "Malone Hoard" from Danesfort House contained 19 polished stone axes.
Individual evidence
- ↑ von Rad 1979, p. 1030.
- ↑ von Rad 1979, p. 1031 ff.
- ^ Rott fossil site near Bonn. .
literature
- Gabriel Cooney, Stephen Mandal: The Irish Stone Ax Project Monograph I , Bray, Wordwell 1998.
- Ulrich von Rad: SiO2 diagenesis in deep sea sediments. Geologische Rundschau, Vol. 68, No. 3, pp. 1025-1036, Springer Verlag, Berlin / Heidelberg (PDF file; 853 kB)
Web links
- Neolithic crafts and skills. Porcelain stone axes from the Ulster Museum