118 
Mr Brooke on three Neiv Species of Lead-ore 
Count Bournon has described the first merely as a variety of 
carbonate of iead. The second he calls rhomboidal carbonate, 
and describes it as dissolving more readily in nkric acid, and 
with greater effervescence than common carbonate. Its pri- 
mary form, he supposes to be a rhomboid of 60® and 120°. 
The third species has been called by Mr Sowerby, in his Bri- 
tish Mineralogy, Green Carbonate of Copper. 
The difference between the external characters of this third 
species and green carbonate of copper, and between that of the 
two first species and any carbonate of lead I had seen, induced 
me to dissolve some of the rhomboidal crystals in nitric acid. 
The effervescence was considerable, as described by Count Bour- 
non ; but I was surprised to observe, after the effervescence had 
ceased, a white insoluble residuum, which, on examination, 
proved to be sulphate of lead. 
In consequence of the observation of this fact, and of the as- 
sociation generally on the same specimen of the three varieties, 
or some two of them, I have examined them all, and I believe 
the following results will be found correct : 
The Sidphato-^carhonatecoxmst^ 0^1 atom sulphate 
1 carbonate 
Effervescence, while dissolving in nitric acid, scarcely percep- 
tible. 
Specific gravity, 6.8 to 7. 
Hardness nearly as sulphato-tri-carbonate. 
Colour whitish, bluish, and greenish-grey, sometimes ap- 
proaching to apple-green. The crystals I have seen are seldom 
distinct, always minute, and aggregated together lengthwise, 
presenting a character approaching to fibrous. 
From the measurements taken by the reflective goniometer 
on two cleavages ; from the character of some of its secondary 
planes ; and from the observation of its cleaving more readily in 
one particular direction than in any other, I conceive its primary 
form to be a right prism, whose base is an oblique-angled paral- 
lelogram of 59° 15' and 120° 45'. But the crystals I have, are 
too imperfect to determine this point with precision, or to give 
the height of the prism. 
j- of lead. 
The Sidphato-trUCarhonatc consists of 
1 atom sulphate ) p . , 
3 — 
