139 
Jrom Wanlockliead and Lead Hills. 
crystals of nitrate of lead till at the end of twenty-four hours. 
Under the action of the blowpipe, it did not decrepitate like the 
carbonate, and yielded an orange-coloured globule, which is one 
of the distinctive characters of the murio-carbonate. 
The mineral which I have now described, crystallises in hexa- 
gonal plates, bevelled on the edges, but imperfectly formed. 
The only detached crystal of it which I could examine with 
the reflective goniometer, is shewn in the annexed sketch. 
Incidence of P upon M, 90° 0' 
p ay 90 0 
P by 110 50 
P c, 127 40 
P fy 110 50 
P 125 22 
P gy 120 0 
P dy 120 0 
M ay 120 0 
The faces corresponding to a, 5, c on the right-hand side of 
the crystal have the same inclination to P as a, 5, c. 
The crystal cleaves parallel to the face M, and with very great 
facility parallel to P,'the laminae never being perfectly united, and 
exhibiting that high lustre which always arises from this cause. 
The plane which passes through the two resultant axes, or 
the centres of the two systems of rings, is parallel to M, and per- 
pendicular to P, and the principal axis of double refraction is 
negativCy and at right angles to P, the red ends of the rings 
being inwards, or nearest the principal axis. 
The primitive form appears to be a right prism, having 
rhomboidal base, with angles of 120° and 60°. The interior 
organization of the crystals is still more imperfect than their ex- 
ternal form. Different parts of the plate have their axes lying 
in different directions, and the crystals are sometimes intersect- 
ed by oppositely crystallised veins, like the specimens of Arra- 
gonite which I have represented in the First Number of this 
Journal. 
As the mineral now described was obviously different from 
all the common ores of lead, I was induced to believe that it 
was either the murio-carbonate of lead, or an entirely new ore. 
It resembled the murio-carbonate in the difficult solubility of 
the white powder, and in the orange button which it yielded 
with the blowpipe ; wliiJe it differed from that mineral in its co- 
