ROGERS. | Minerals of the Galena-Joplin District. 499 
Leadhillite. 
The following description of the mineral leadhillite, occur- 
ring at Granby, is taken from Pirsson and Wells’s paper in 
the American Journal of Science :” | | 
‘“‘The crystals occur in thick hexagonal tables or slender 
hexagonal prisms, which are grouped together in parallel 
position and line cavities consisting of masses and crusts 
apparently pseudomorphous after galena. In color, leadhill- 
ite varies from colorless in the smaller crystals to a clear 
sea-green in the larger ones. 
‘‘The crystals, apparently simple hexagonal prisms, are 
monoclinic crystals consisting of the forms c(001)OP; 
a,(100) =P; \(110)oP. Other forms occurring are as 
follows: e(201)+2Pe; u(201)-2P~; 4q(414)+P4; 
u(418)+4P4. Figure 73 (after Pirsson and Wells) repre- 
sents one of the simpler combinations. 
‘Twinning on the unit prism is very common, and, in some 
cases, it appears as if the composition face is the basal plane. 
‘‘Cleavage parallel to the basal plane is very perfect and 
easily produced. The luster of this face is pearly. The 
hardness is nearly 3. The specific gravity is 6.54. Etch- 
figures produced on the cleavage plates by very dilute nitric 
acid show monoclinic symmetry. The chemical composition, 
which until this time had been somewhat doubtful, is de- 
termined by the following analysis: 
Calculated for 
Found. Ratio. 4PbO-2CO2-SO3- H20 
SOsaee eer ae SOI AR rc ne Gate a UEOOe PR MAR MAS ek ae Uo583 
CO ere a 4 Coys Ui i seic ok Sie ae a eek VR i RR th Hae Ue 8.29 
DORMS tees SORA A isc rcs net Ale (Ane eon ate ereua eee: 82.49 
BELO SE Mrespae eee RG State Outi we Robe. TROQE ME Sides 0 1.69 
100.00 100.00 100.00 
‘‘These results show that the mineral has the formula 
PbSO,-2PbCO,-Pb(OH)., which is the composition suggested 
by Groth.”’ 
Leadhillite also occurs pseudomorphous after galena and 
calcite, as described by Foote. Granby is the only locality 
for this mineral. 
20. Pirsson and Wells: Amer. Jour. Sci., (3), XLVIII, pp. 219-226, 1894, 
21. Warren M, Feote: Amer. Jour. Sci. (8) J, pp. 99, 100, 1895, 
