Bryntail mine, Central Wales Orefield. It is unusual to find such a well formed specimen of dolomite in the Central Wales Orefield. It is more usual to find ferroan dolomite. The specimen has a very uniform construction and the curved surface and rhombohedral habit is very obvious. The colour is greyish white and there is no sign of brown or other colours in this and other similar specimens found on the mine spoil heaps.