In ancient times, stones were considered to be holy and magical objects, homes to spirits and the Gods. In local Welsh legends and folklore it is said that the Preseli Bluestones possess healing and magical powers. It is no surprise then that this rare stone should be used for this Island's greatest megalithic structure - the very root of all our architecture. Preseli Bluestone Geology Preseli Dolerite (Bluestone) is a Metamorphic Igneous rock made up of Plagioclase Feldspar and Augite and is a Pyroxene mineral (calcium magnesium aluminosilicate. Ca, Mg, FE, AI, (Al,Si,206). It is medium grained dark and heavy rock, harder than granite. Preseli Bluestone tools, such as axes, used by our ancestors to carve granite, have been discovered.