This is a rather unusual specimen that has two major components, Silica SiO2 and Calcite CaCO3 It obviously started life as a Silica geode, but about 30% of the centre has been invaded by a growth of massive calcite. For the main, the inner cavity is lined with miniscule quartz crystals, with a number of "stalks " composed of almost microscopic druzy quartz crystals. There are quite a number of very small doubly terminated quartz crystals, which would put them in the category of "Herkimer diamonds. There are also quite a number of very small calcite rhombs' "In the small inset picture a small rhombohedral calcite crystal is mounted on one of those herkimer type crystals. The specimen is from Dulcote hill in the Mendip Hills. from workings that closed in the mid 1970s.