Primitive Crystallized Carbonate of Lead

This specimen is a great curiosity, as it does not seem to have been before known that Carbonate of Lead crystallized in rhomboidal prisms. Haüy seemed to think the octaëdron to be the primitive figure ; indeed we have been able in some specimens to trace all but four of his fractures; this however appears to be preferable, as it bears some analogy to Sulphate of Barytes, which has a rhomboidal primitive only differing in the angles, otherwise often producing similar modifications, which vary according to the nature of the substance, The angles of this rhomboidal prism are 76° and 104°; the laminae are very distinct on all the faces. Carbonate of Lead, when we find it so nearly resembling this substance, may soon be discovered by the help of the blowpipe in procuring a little globule of Lead from it on Charcoal. They both form a nearly opaque glass; but if the heat is continued, the one will of course be reduced to Lead, and the other will remain unaltered.