﻿H. A. Wheeler — Artificial Lead Silicate. 273 



lead-silicate were found as linings of irregular cavities. The 

 gangue of the ore is a magnesian limestone, which though 

 mostly removed by dressing, is still present in appreciable 

 quantities in the roasted ore and shows in the analyses. Asso- 

 ciated with the galena is more or less pyrite, and a very small 

 but persistent amount of nickel and cobalt ; especially the 

 former, probably as siegenite, though it is generally not to be 

 detected by the eye. 



My examinations, as far as they go, largely confirm those of 

 Dana and Penfield. In one group of dark-red crystals, of 

 rather feeble lustre, the individual members measure from 30 

 to 40 mm in length and thickness, and their -analysis is given 

 below. Another group of crystals furnish dimensions of 8 to 

 15 mm , while they have a highly vitreous luster and are of a 

 clear brownish-red color. They all seem to consist of one type 

 of crystal, that is generally very perfectly developed, made up 

 of two trigonal prisms and the basal pinacoid. One of the tri- 

 gonal prisms is largely developed and is very prominent, while 

 the faces of the other trigonal prism are much smaller and in 

 some cases are scarcely apparent. The fracture is decidedly 

 resinous and the streak yellow, while the hardness is 3. 



Analyses of the large, dark, translucent and the small, clear, 

 light colored crystals are herewith appended, which agree with 

 those of Penfield in showing that it is essentially a lead silicate. 

 The finely disseminated magnetite alluded to by Penfield I also 

 found, but removed it, after finely grinding in an agate mortar, 

 with a magnet. It probably comes from the scales that drop 

 off from the iron tools that are so freely used at the fusion 

 stage of the roasting process. 



Coarse Crystals. Fine Crystals. 



SiO a 17-11 18-51 



PbO 73-66 72-93 



Fe 2 3 0-80 1-31 



A1 2 3 0-53 0-62 



CaO 2-35 1-66 



MgO 0-22 0-20 



CI 0-08) ( undet. 



Na 2 2-22 [ 5-36tf - " 



NiO 3-06 



100-03$ 95-23$ 



In the analyses given by Penfield, the iron is given as FeO; 

 as it plays so small a part in the composition, while the color 

 of the specimens are all either red or brown, no special exam- 

 ination was made to determine the condition of the iron and it 

 was assumed to be in the form of Fe 2 3 . 



Department of Mining and Metallurgy, Washington University. 



