G94 SCIENTIFIC RECORD FOR 1885. 



De Schulteii describes the foruiatiou of a hydrous phosphate of iron 

 Fe2P208+4Aq. in rose-colored crystals, corresponding to the mineral 

 strengite ; strengite, however, is orthorhombic in crystallization, while 

 these crystals were niouoclinic. The same author has formed a magne- 

 sium hydrate (the mineral brucite) in six-sided tabular, or short pris- 

 matic crystals, optically uniaxial ; also a similarly crystallized cadmium 

 hydrate. Vater describes crystals of hematite, formed in the fire Hues 

 in the chemical manufactory in Schonebeck, near Madgeburg. Their 

 formation is explained by the presence of pyrite and sodium cLloride 

 in the coal employed; from these iron chloride for;us, which, in the cooled 

 parts of the flues, is decomj)osed by the escjaping water vapor with the 

 result named. The crystals attain a magnitude of 2 millimeters. 



The natural alteration of minerals is another chapter of chemical 

 mineralogy which has received some attention. F. W. Clarke and J. S 

 Diller have studied the changes of the topaz of Stoneham, Me. Tlieir 

 investigations cover both the chemical and microscopical sides, the sec 

 tions under the microscope showing the progress of the alteration and 

 the analyses what the results are. A series of analyses trace the 

 changes from the unaltered topaz to the final product, massive or folia- 

 ted potash mica (damourite). The fluorine lost by the topaz is believed 

 by the authors to have led to the formation of the fluorite, herderite, 

 triplite, and apatite of the locality. Cathreiu has studied the changes 

 undergone by the garnets of the amphibole schists of the Tyrolean Alps. 

 The alterations described are very various, leading to the formation of 

 scapolite, of epidote, oligoclase, hornblende, saussurite, and chlorite. 

 Another interesting case of pseudomorjihism is that of turquois after 

 apatite. The specimens were from Taylor's ranch on the Chowcilla 

 River, in Fresno County, California, and they are described by G. E. 

 Moore and V. von Zepharovich. The crystalline forai of the original 

 mineral is distinct, a hexagonal prism, but the substance consists of a 

 greenish-blue or bluish-green aggregate of minute spherulites with 

 radiated and concentric fibrous structure. An analysis showed it to be 

 a hydrous phosphate of alumina, with a little iron, and about 8 per cent, 

 cupric oxide, corresponding approximately to an analysis by Church of 

 a turquois from Nichabur. Still another case of pseudomorphism im 

 portant especially in its geological relations is that of the thmoUte, the 

 crystalline calcareous tufa of Lake Lahontan, in Northwestern Nevada. 

 This occurs, as is well known, on an immense scale, and the question of 

 its origin is a vital one in the explanation of the geological changes of 

 the region. It was referred to gay lussite by Clarence King, but the 

 writer shows from a crystallographic study of the forms remaining that 

 it does not correspond to any known mineral, having a form which can 

 be approximately referred to an acute tetragonal pyramid. The simi- 

 hirity of this to the pseudomorphs of lead carbonate after phosgenite 

 (chloro-carbonate of lead) has suggested the hypothesis that the origi- 

 nal mineral may have been an isomorphous chloro-carbonate of calcium. 



