Dolerite is an igneous rock formed below the Earth's surface. Dolerite is a form of basalt containing relatively little silica (mafic in composition). It is made up of  tiny crystals which are interlocking and randomly orientated. Preseli Spotted Dolerite (Bluestone) is a medium grained dark and heavy rock, (harder than granite).The rocks at Stonehenge (UK) are made from Dolerite bluestones and were placed there around 2300 BC. It is assumed that there were about 80 of them originally, but this has never been proven since only 43 remain. Dolerite was used by the Stonehenge constructors as they believed in stones properties. GAEA is believed to be the only company who facets Dolerite so that it can be used in rings and pendants.