G. F. Kuns — Mineralogical Notes on Brookite, etc. 829 



Art. XLTI. — Mineralogical Notes on Brookite, Octahedrite, 

 Quartz and Ruby ; by George Frederick Kunz. 



An interesting discovery of minerals was made at Placer- 

 ville, Eldorado Co., California, by Mr. James Blackiston, in a 

 quartz ledge running north and south and dipping eastward 

 about 45° to 50°. The rock of the ledge is partly decomposed 

 and partly compact, and is traversed for perhaps a hundred 

 feet by a vein of crystallized quartz varying from six to four- 

 teen inches in width. This vein is also decomposed and filled 

 in with a reddish earth and sand, and can be dug into with a 

 stick or board. It is full of quartz crystals, of all sizes from 

 that of a man's finger up to remarkable dimensions, some of 

 them weighing as much as 80 or 90 pounds. Several of these, 

 over fifty pounds in weight, were pellucid and free from flaws : 

 while others have peculiar interest from remarkable inclusions 

 of chlorite, three to five millimeters in thickness, at several 

 depths in the crystal — thus marking successive stages of crys- 

 tal-growth, and making very striking " phantoms," generally 

 of green chlorite, or white quartz layers. Of still greater 

 interest, however, are other quartz crystals, two to four inches 

 long and half that amount in diameter, containing at and near 

 their centers inclusions resembling groups or clusters of dolo- 

 mite or siderite crystals, cream-white to brown in color, and 

 consisting of many curved rhombohedra from two to four 

 millimeters in diameter. On breaking the specimens, how- 

 ever, the curious fact appears that these groups are hollow 

 cavities in the quartz, the spaces being lined with a layer of 

 chalcedony, or when brown, occupied only by a brown siliceous 

 material. This would indicate that the original mineral must 

 have been siderite or ankerite, afterward covered up by suc- 

 cessive growths of the quartz, and in some manner decom- 

 posed during that process. 



After receiving some of these specimens, the present writer 

 detected a small crystal of octahedrite adhering to one of the 

 small quartz crystals. Search was then instituted at the local- 

 ity, which resulted in the discovery of a number of crystals of 

 both octahedrite and brookite, some loose and some attached 

 to the quartz. The octahedrite is in splendent crystals, from 

 two to five millimeters in length, and varying in color from 

 brown to almost a dark blue. Their form is that of the unit 

 pyramid slightly distorted by horizontal striation. 



The brookite is similarly implanted on the quartz, and partly 

 or wholly overgrown by it, so as in some cases to be a true 

 inclusion. The crystals are tabular, about two millimeters 

 broad and one-fourth of a millimeter in thickness. Their color 



