Quartz

Quartz

There are many badly formed prismatic crystals of quartz, SiO2 lining this cavity in sandstone. The crystals are colourless, but many appear to be dull orange in  colour, due to a dusty coating of possibly an iron mineral. The specimen is from Tan y Foel quarry at Cefn Coch in Powys. The quarry is in the Penstrowed grits formation of Mid Silurian age.