Geology and Mineralogy. 73 



Pseudobiotite. Knop closes an interesting article on the 

 composition of biotite, in which he gives analyses of varie- 

 ties from several localities, by describing an altered kind under 

 the name of pseudobiotite. It occurs in scales in the crystallized 

 limestone of the Kaiserstuhl. The mean of two analyses gave : 



SiOo Ti0 2 Al 8 0s Fe 2 3 Mn 2 3 ? MgO K 2 H 2 



35-91 1-15 15-18 1085 0-89 22-80 2"90 10-77=100-45 



The author does not regard it as a definite compound. — Zeitschr. 

 Kryst., xii, 607, 1887. 



Geiqualandite. Described by G. Grant Hepburn as a hydrous 

 ferric silicate pseudomorphous after crocidolite from Griqualand 

 West, South Africa. The supposed new mineral, however, was 

 obviously the siliceous material extensively used as an ornamental 

 stone (tiger-ej^e) which consists of silica more or less impregnated 

 with the yellow iron oxide derived from the alteration of the 

 original crocidolite. — Chem. News, May 27, 1887. 



Manganotantalite. — A member of the tantalite-columbite 

 group of minerals described by Arzruni from the Uralian gold 

 washings. It is known from a single crystal only, which has in 

 general the habit and dimensions of ordinary columbite. The 

 specific gravity was found to be 7'37, and the color, nearly black 

 by reflected light, was brown to orange-red by reflected light in 

 thin splinters. An analysis by Blomstrand gave : — 



Ta 2 5 Nb 2 5 Sn0 2 , W0 3 FeO MnO CaO ign. 



79-81 4-47 0-67 1:17 13-88 0-17 (0-167)=100-33 



This corresponds to the formula HMnTaj0 6 + FeNb 2 6 . The 

 mineral is related therefore to the manganese tantalo-niobate 

 from Branchville, G. = 6'59, analyzed by Comstock (this Journal, 

 xix, 131, 1880), and to the mangantantalite, G. = 6 - 3, of Norden- 

 skjold (3d Appendix to Dana's Mineralogy, p. 118). It contains, 

 however, much more tantalum and correspondingly has a higher 

 specific gravity than either of these minerals. — Verh. Muss. Min. 

 Ges., 1886. 



Ceistobalite. — This name has been given by vom Rath to some 

 small octahedral crystals found at the tridymite locality of Cerro 

 San Cristobal, near Pachuca, Mexico. They are in part spinel-like 

 twins, and occur intimately associated with the tridymite, in cavi- 

 ties in the andesite. An analysis showed them to consist essen- 

 tially of silica, and the author is uncertain whether to regard 

 them as a new form of crystallized silica or as pseudomorphs 

 after some undetermined mineral, but inclines to the latter 

 opinion. An examination by Bauer showed them to possess a 

 rather strong abnormal double refraction. In this respect they 

 are like the unexplained cubic crystals of silica found by Lasaulx 

 on the sulphur of Girgenti and called melanophlogite. 



11. Uraninite and monazite from Canada; by G. C. Hoffmann. 

 (Communicated). — These minerals were found at the Villeneuve 

 mica veins, situated in the township of Villeneuve, Ottawa county, 

 Quebec. The workings are on what has been described as a 



