I propose to add one more account to those which have already been published of this mineral. It is described as a rhombie mineral in Dana's Mineralogy and other standard works. Latterly it has been described by Reusch as an anorthic mineral, from National Belie Mine, Red Mountain, Colorado, in the Jahrbuch für Mineralogie, 1887, Bd. II. Now I describe it as monoclinic, principally from a study of that variety of it which occurs in Anglesey, of which an account was published by Dr. Percy in 1875 in his Metallurgy, Vol. "Fuel."