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

90 mm x 80 mm x 13 mm thick

KO107  Killaloe Opal slab

Dimensions at widest points approximately 200 mm x 130 mm x 70 mm thick

105 mm x 85 mm x 9

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