118 Mr. Brooke on a New Lead Ore. [Aus. 
small degree from that which I have given. A fragment of 1-4 
grain, which is more transparent than the general mass of the 
substance, has indicated a specific gravity of 5°43. 
It scratches sulphate, but is scratched by carbonate of lead. 
For the purpose of enabling me to describe the crystalline 
form more accurately than I could have done from my own spe- 
cimens, Mr. Sowerby has favoured me with a couple of small 
crystals whose form is rudely represented 
by the annexed hastily drawn figure. 
The cleavages are parallel to the planes 
M and T. That parallel to M may be 
effected almost by pressure between the 
fingers. I have not observed any trans- 
verse cleavage, but as the plane P is at 
right angles to M and T, and as the plane 
M does not meet the planes 0’ and T at 
the same angle, the primary form may be 
regarded as a right prism whose base is 
an oblique angled parallelogram. 
The measurements are as follows, the letters b’, a’, T’, and M’, 
being placed above the edges of the planes to which they relate: 
Mom. 25 Wicty . acid Need 102° 457 
TRE HOO GRACE <3 -- 104 50 
Ce Pi aes vee koh es 120 30 
FT Nees eee ne es 90 0O 
Lin BE HARB POR Wea SO 161 30 
WO Oni: ter a ae Re ohn tt i Dae 
Dict x0 etn pm 3 Fs bere e Wile ae 102 45 
SG, NSM rene v's whe eke Sen eee oR > "G 
If we suppose the plane 6 to result from a decrement by one 
row on the acute lateral edge of the prism, the terminal edge of 
the plane M would be to that of plane T nearly as 11 to 23, and 
if the planes c and c’ are produced by a decrement by one row 
on the terminal edges, the height of the prism will be to the 
greater terminal edge as 13 to 23 nearly. 
The specimen I possess is so sinall, and so little of it is, per- 
fectly pure, that I have not been able to submit more than a few 
grains to analysis. The result of this has given the following 
proportions of the constituent parts of the mineral : 
Dulpnaie q@iaade. ws, .'s dss sis aj voice POP i 
Onide oljcopper: <j. uy fs 5's... cant 18-0 
Loss by heating...... Ahad, ci n.0'o as ene, EY 
98°1 
As there was not any effervescence perceptible during the 
solution of the mineral in sulphuric acid, the loss by heating 
must have been occasioned by the loss of water only ; and if we 
