'Preseli Bluestone' is a form of Spotted Dolerite. It is an igneous rock containing white spots of the mineral Plagioclase Feldspar. The rock is medium grained, and has a slight blue tint in colour. The samples originate from the 'Preseli Hills' region of Wales, and were transported as large blocks by a Quaternary glacier & deposited as glacial erratics when the ice melted.
The 'Preseli Bluestone' is particularly famous as it was one of the rocks used in the construction of Stonehenge. Other items of Archealogical interest iclude axe heads which have been found to be made from Preseli Bluestone.