454 General Notes. 
cite crystals are developed. Other dykes from the northern portion 
of the island appear to consist of hornblende and biotite picrites. 
In one case newly formed, almost colorless hornblende is described 
as forming a cement between crystals of original hornblende, in a 
manner analogous to the quartz cement in indurated quartzites. 
MINERALOGICAL NEws.—The diamonds found in the Province 
of Minas Geraes, Brazil, are associated with the oxides of titanium, 
martite, monazite, and xenotine. They are usually found in qua- 
ternary alluvial deposits, but have their origin, according to Gor- 
ceix,' in the itacolumites and mica schists which are archean. In 
these rocks they occur in deposits analogous to those of topaz, ana- 
tase, rutite, etc. All these minerals occupy well-defined bands in 
the itacolumite, and are original in it, and are not derived from 
some older rock, whose detritus supplied the material for the 
itacolumite and the mica schist. This explanation of the origin 
of Brazilian diamonds is quite different from that offered? in the case 
of diamonds of the African and American fields. Polianite, the 
anhydrous manganese dioxide, has heretofore not been found in 
sufficiently well-crystallized specimens to admit of a satisfactory 
determination of its crystallographic constituents. The investiga- 
tions? seemed to point to an orthorhombic symmetry for it. Messrs. 
Dana and Penfield‘ have recently proven it to be tetragonal and 
isomorphous with cassiterite, with a:e==1:.66467. The crystals 
examined are composite, being composed of several tetragonal indi- 
viduals which produce a body with an orthorhombic habit. Their ' 
specific gravity is 4.992, and their composition as follows :— 
MnO o Fe,0, SiO, H,O Insoluble. 
80.81 18.16 16 36 .28 16, 
revealing a very pure manganese dioxide. In the basalt from 
the neighborhood of Périer (Puy de Dôme) are little veins of clayey 
material® in which are imbedded crystals of augite and lozenge- 
shaped flat plates of feldspar. The plates are sections parallel to 
the clinopinacoid, bounded by the planes oP and Px equally 
developed. They are frequently twinned with oo Poo as the composi- 
tion face——Jannetaz® has analyzed uranite from the Island of 
Madagascar, with this result :— : 
Igelström” has discovered a manganese, rich and antimony- 
P.O, NO, Fe,0, CaO Loss (water). 
14.93 55.08 1.365 6.51 _ 22.08 
* Amer. Jour. Sci., March 1888, p. 243. 
5 Lévy: Bull. d. 1. Soc. Franç. d. Miner., X., 1887, p. 69. 
6 Ib., p. 47. 
1 Bull, Soe. Franç. d. Min., ix., 1887, p. 218. 
