Polished fossil Oncolite. ONC111 #brecciated PU133 Purple Chalcedony slab

PU133  Purple Chalcedony slab

Dimensions at widest points approximately 240 mm  x 160 mm x 10 mm thick

Dimensions at widest points approximately 250 mm x 145 mm x 10 mm thick

A trade name for metamorphosed magnesian tholeiite (basalt)

Polished fossil Oncolite. ONC111 #brecciated PU133 Purple Chalcedony slabONC111. Fossil Oncolite polished slab. From the Miocene "Trealla Limestone" north of Carnarvon, Western Australia . Age is approx. 15 million years. Dimensions at widest points approx. 140 mm x 100 mm x 6. 5 mm thick. Weighs 204 grams. Oncolite is a limestone composed largely of oncoidsrounded, coated grains that grow as thin layers of lime mud accumulate around a tiny nucleus (such as a sand grain or shell fragment) under microbial influence. Formed