MINEBALOGY. 227 



Chttech, Prof. A. H. Beryls and Emeralds. Quart. Journ, Sci. 



no. xliv. pp. 505-508. 

 A general description of these gems, with special reference to Mr. 

 Williams's recent researches on the colour of the emerald. 



Clemencin, p. M. La Wollastonita no es el bisilicato de Cal. [Wol- 



lastonite not a bisilicate of lime.] Kevista Minora, xxv. pp. 



223-225. 



Calls attention to the confusion introduced by calling such silicates 



as WoUastonite bisilicates. The formula of this species may be written 



3CaO . 2Si03, in which case it corresponds to a sesquibasic silicate of 



lime ; or it Djay be written CaO . SiO^, which is the formula of a neutral 



silicate. P. W. R. 



Cleve, p. T. Om mineralet Cuban. [On Cubane.] Geol. fdren. 



Stockholm Forhandl. bdt. i. p. 105. 

 Gives three analyses, by T. 0. Carlin, A. W. Brodin, and G. Lind- 

 strom, of Cubane from Tunaberg and Kafveltorp, both new locahties. 

 The formula deduced is (2reS . Cu,S)re,S3. G. A. L. 



. Om koboltkis (Linneit) frSn Bastnas och Gladhammar. [On 



cobalt-pyrites (Linncite) from Bastnas and Gladhammar.] Geol. 



fdren. Stockholm Forhandl. bdt. i. pp. 125, 126. 



Analyses of this mineral from both localities are given, the resulting 



formula being ^8,^383. Gladhammar in SmSland is a new locality for 



Linncite, where it was found by G. Lindstrom. G. A, L. 



Cooke, Josiah P., Jr. The YermicuKtes : their crystallographic and 

 chemical relations to the micas ; together with a discussion of the 

 cause of the variation of the optic angle in these minerals. Proc. . 

 Amcr. Ac. n. ser. vol. i. pp. 35-67, with 9 woodcuts. Reprinted 

 in Phil. Mag. no. 312, pp. 241-272. Full abstract in Amer. 

 Joum. ser. 3, vol. viii. pp. 420-437. 

 Uses Vermiculite as a family-name to include the minerals Jefferisite, 

 Culsageeite, and Hallite. These are hydrous silicates, forming a group 

 parallel with the micas, and differing from the magnesian micas chiefly 

 in containing a definite number of molecules of water of crystallization. 

 Seeks to show that the remarkable exfoliation of the vermiculites 

 when heated is due to the escape of this water. Jefferisite, Culsageeite, 

 and Hallite correspond respectively with the two varieties of Biotito 

 and with Phlogopite. Describes twin-forms, and refers to this twin- 

 ning in explanation of the great variation in the optic angle exhibited 

 by the vermiculites, ripidolites, and certain micas. Speculates on the 

 molecular structure of such crystals. By process of twinning, uniaxial 

 crystals of hexagonal type may bo constructed from rhombic crystals 

 with angles of 60° and 120°. Suggests that hexagonal crystals of other 

 minerals may bo similarly developed. 



The Phn. Mag. reprint is prefaced by a letter calling attention to the 

 optical results. In Amer. Joum. vol. viii. p. 139, is a note acknow- 

 ledging the priority of somoM)f Reusch's researches on circular ^wlariza- 

 tion. F. "W. R. 



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