Polished fossil Oncolite slab. ONC115 oldest agate in the world PA277 Pilbara Agate

PA277  Pilbara Agate

190 mm x 100 mm x 90 mm thick

Approximate dimensions at widest points 170 mm  x 75 mm  x 55 mm thick

OJ192  A rough rock

Polished fossil Oncolite slab. ONC115 oldest agate in the world PA277 Pilbara AgateONC115. 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. 170 mm x 70 mm x 7. 5 mm thick. Weighs 211 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