13S Dana and Pmfield — Mineralogical Notes. 



2. — An artificial crystallized Lead Silicate. 



We are indebted to the late Professor Silliman for a speci- 

 men of an artificial crystallized lead silicate, which had been 

 obtained by him from the Desloge Lead Company, Bonne- 

 terre, St. Francois County, Missouri. The specimen consists 

 chiefly of a brownish-red substance with resinous luster some- 

 what resembling sphalerite, associated with octahedral crystals 

 of magnetite and cleavable galena. In small cavities in the 

 mass and over the surface are numerous crj'stals, mostly stout 

 hexagonal prisms, which, as is proved later, consist of the same 

 material as the mass of the specimen. These crystals in color 

 and form very closely resemble much of the vanadinite of 

 Arizona, and, before the history of the specimen was known, 

 they were referred to that species almost without question. 

 Later, however, it was learned that the specimen was artificial 

 in origin, and according to the chemist of the company was a 

 lead silicate. A preliminary chemical examination proved 

 that to be true, and a complete analysis was accordingly made 

 of the hexagonal crystals and also of the massive substance. 



The crystals spoken of vary in length and thickness from 1 

 to 3 mm . They show ordinarily only the planes of the unit 

 prism / (1010) and the basal pinacoid (0001) ; rarely, how- 

 ever, the basal edges of the prism are rounded and in a few 

 instances distinct planes were observed. The best defined of 

 these gave an approximate angle of 50° on the basal pinacoid 



O^p, 0001/vloTl, =50°. 



This gives as the length, of the vertical axis 



c= 1-032. 



A second pyramidal plane {q) gave an angle on the base of 25°, 

 which corresponds tolerably to the symbol f- (2025), required 

 25° 29'. Apparently these pyramidal planes are holohedrally 

 developed, so that the crystals would then be referred to the hex- 

 agonal system proper, but the material was too scanty absolutely 

 to prove this point. There is some reason to doubt it, however, 

 for on the other side of the same specimen, distant from them 

 hardly an inch, are a few crystals apparently of the same ma- 

 terial, but of quite different form. These are thin tabular 

 crystals showing only the basal pinacoid and a rhombohedron; 

 the measured angle for this is 67°, which, referring it to the 

 above axis, would give it a symbol 2B, or tt (2021). The cal- 

 culated angle is 



Oy\2B, 0001 yv 2021, =67° 12'. 



