Polished fossil Oncolite slab. ONC114 beryl Chinese Writing Stone is a

Chinese Writing Stone is a porphyritic basalt (porphyry) with groups and rosettes of plagioclase feldspar

Dimensions at widest points approximately 80 mm x 55 mm x 40 mm thick

DO173  Dendritic Opal slab

One edge slightly unpolished

Dimensions at widest points approximately 90 mm x 75 mm x 8 mm thick

Polished fossil Oncolite slab. ONC114 beryl Chinese Writing Stone is aONC114. 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. 150 mm x 100 mm x 7. 5 mm thick. Weighs 241 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