MINERALOGy. 245 



Eammelsberg, C. Die Fortschrittc der Mineralchemie wie sio seit 

 fiinfzig Jaliren aus Poggendorff's Annalen sicli crgaben. Pogg. 

 Ann. Jubelband, pp. 381-407. 

 A review of the progress of mineral chemistry as set forth in Pog- 

 gendorff's Annalen during the past fifty years. 



. Ueber die krystallographischen nnd chemischen Beziehung 



natUrlicher Schwefel-Arsen- und Schwefelarsenverbindungen. Ber. 

 deutsch. chem. Ges. pp. 152-156. 

 It is known that RS^ is isomorphous with RASa ; but R and As may 

 themselves be isomorphous ; therefore the compound RSg may be 

 ismorphous with R„As„. Hence the natural arsenides which contain 

 sulphur may be referred to the general expression RS^ . a'R^As,,. If 

 cr=l, andm:n=l:2, we obtain the formula for arsenical pyrites, 

 nickel- glance, and cobalt-glance. The natural compounds containing 

 RSj,, or Ra,As,„ or isomorphous mixtures of these, form two hetero- 

 morphous classes of minerals, the one cubic and the other rhombic, 

 which may be called respectively the pyrites and the marcasite group. 



F. W. R- 



Ratu, G. vom. Miueralogische Mittheilungen. Pogg. Ann. Bd. clii, 

 pp. 1-42, plate ; and Amer. Journ. ser. 3, vol. viii. p. 319. 



A continuation of the author's mineralogical communications. Con- 

 tains the following essays : — Contribution to the knowledge of the 

 crystallization and twin-formation of tridymite ; a remarkable crystal 

 of calc-spar from Lake Superior ; a peculiar growth of rutile and iron- 

 glance ; artificial crystals of coj^per ; hypcrsthene from Mont Dore, in 

 Auvergne ; and on Poresite, a new mineral of the zeolite family, from 

 the granite veins of Elba. Also notes on andesine from trachyte of 

 Ecuador ; cordierite from Laach ; and yellow augitc from Vesuvius. 



F. W. R. 



. Einige Studien iiber Quartz, Kupferkies, und Albit. Pogg. 



Ann. Jubelband, pj). 538-549, with part of a plate. 



Describes a peculiar kind of twinning in amethyst ; remarkable 

 cr}^stals of quartz from Madagascar; twins of copper-pyrites from 

 Griinau on the Sieg ; and crystals of albite in a volcanic rock. The 

 albite occurs, with orthite, in fragments of trachyte in a conglomerate 

 from the Langenberg in the Siebengebirge. F. W. R. 



. Ueber die chemische Zusammensetzung der Plagioldasc 



(triklincr Feldspathc). [Chemical composition of plagioclase.] 



Monatsb. k. prcuss. Ak. "NViss., Jan., pp. 20-32. 



Analyses of plagioclastic felspars from the volcanic rocks of the 



Cordilleras of Ecuador. They include plagioclase from the quarlz- 



andesite of Mojanda, from the andcsite of Pululagua, and from the 



hornblende- andcsi to of Guagua-Pichincha and of Pomasqui. F. \V. R. 



. Su la Forcsite, nuovo miuerale della famiglia delle Zcoliti 



rinvenuto nelle geodi tormalinifere dell' Isola d' Elba. [On Fore- 

 site, a new mineral of the Zeolite family found in tourmaliniferous 



