The main rock types of the Campanian Mishash Formation in Israel are: (1) homogeneous chert; (2) chert spheroids; (3) heterogeneous (breeciated) cherts; (4) porcelanites. Zones of preferred orientation were detected in the heterogeneous cherts, and two alternative models are suggested to explain both the breeciation and the formation of preferred orientation. The cherts in the Mishash formation are mostly products of early replacement of carbonate and sometimes phosphate sediments. Apatite seems more resistant to silicification than calcite. Some of the siliceous rocks (homogeneous cherts, spheroids) may have been formed by primary precipitation of silica.

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