Diorite n. (Min.) An igneous, crystalline in structure, consisting essentially of a triclinic feldspar and hornblende. It includes part of what was called greenstone.
... no manner of doubt that it was a so- called demi-dolmen, a tribal ossuary of neolithic man. Not only is it quite in character with his megalithic remains scattered over the country, but treasure-seekers who in digging displaced and brought down one of the side slabs found two diorite axes, one of which I was fortunate enough to secure. Persons in Gaulish or post-Roman times would not have dreamed of going to the enormous labour and attempting the difficult task of forming the sides with stone ... — Castles and Cave Dwellings of Europe • Sabine Baring-Gould