Summary: The description of the new mineral may be summarized as follows:

Villamaninite, a sulphide of copper, nickel, cobalt, and iron, rich in selenium; probably a disulphide (Cu,Ni,Co,Fe)(S,Se)₂. Copper 19, niokel 18, cobalt 7, iron 4, sulphur 50, selenium 112 per cent. Crystalline system cubic. Occurs disseminated in crystalline dolomite as small, ironblack crystals, also as small, nodular aggregates. Lustre dull metallic. Opaque; streak sooty black. Hardness 412. Sp. gr. 4.4–4.5. In the closed tube, gives a sublimate of sulphur and selenium. Soluble in nitric acid, leaving a globule of sulphur. Locality: Cármenas district, near Villamanín, Prov. León, Spain.

In conclusion, we desire to acknowledge our indebtedness to Mr. L. J. Spencer, who determined most of the physical characters of the new mineral, and gave valuable help in the preparation of the manuscript. Selected specimens have been presented to the Mineral Department of the British Museum (Natural History).