Polished fossil Oncolite slab. ONC117 purple chalcedony Dimensions at widest points approximately

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

Weighs: 814 grams

DOT103  Tumble polished Dendritic Opal

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

Annular rings with heart visible

Polished fossil Oncolite slab. ONC117 purple chalcedony Dimensions at widest points approximatelyONC117. 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