Carbonate of Lead

This specimen, lately sent me, by favour of Mr. Laing, from Wanlock Head mines, near Glasgow, shows the disposition of the last mentioned substance to form plated octo-decaëdrons and other modifications, inclinging to the appearance of sulphate of barytes, by forming a sort of truncation on the edges. Thus the left hand figure is truncated on the edges of the original six-sided column, forming six-sided faces: see the dotted lines on the column of the right hand figure, and also the apex which is terminated by six trapezoidal faces. Thus we should have 48 faces if they were regular; this is certainly a curious modification. Mr. Laing judiciously observed, that the sulphuret of lead, or galæna, in most cases, where it is decomposing to form carbonate of lead, has a blue tarnish. It sometimes also becomes dusty or crumbly.