Polished fossil Oncolite slab. ONC117 purple chalcedony 90 mm x 80 mm

90 mm x 80 mm x 13 mm thick

100 mm x 75 mm  x 25 mm

Magnesite (Lemon chrysoprase) rough rock (nodule)

Dimensions at widest points approximately 290 mm  x 170 mm x 9

DOT103  Tumble polished Dendritic Opal

Polished fossil Oncolite slab. ONC117 purple chalcedony 90 mm x 80 mmONC117. 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. 160 mm x 80 mm x 8. 5 mm thick. Weighs 217 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