THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



— ^ 



Art. XXIII. — The Crystal Structures of some Carbon- 

 ates of the Calcite Group; by Ralph W. Gr. Wyckoff. 



The crystal structure of calcium carbonate has been 

 previously studied, using the spectrometer. 1 At the same 

 time measurements were made upon the crystallographi- 

 cally similar iron and manganese carbonates, which indi- 

 cated that they had the same structure as calcite. The 

 present study of the crystals of the calcite group was orig- 

 inally undertaken in the hope that the additional informa- 

 tion which Laue photographs furnish would serve to place 

 the oxygen atoms with considerable accuracy. Some in- 

 formation might thereby be supplied regarding the exist- 

 ence of definite carbonate (C0 3 ) groups of atoms in the 

 crystalline solid. 



The carbonates of calcium, iron, and manganese occur 

 naturally in excellent crystals. Good crystals of magne- 

 site (MgC0 3 ) and especially of smithsonite (ZnC0 3 ) are 

 rarely found. The other members 2 of this "isomor- 

 phous ' ' group of substances are the cobalt salt, which has 

 been found asi a mineral (spherocobaltite) and has been 

 prepared artificially, and cadmium carbonate, which is 

 found in isomorphous mixtures with zinc carbonate. 

 Crystals of nickel carbonate have been made which also 

 seem to belong to this same group. Of these various 

 compounds, however, only individual crystals of calcite, 

 magnesite, rhodochrosite (MnC0 3 ), and siderite (FeC0 3 ) 

 were available for this work. 



The method of study is essentially the same as that of 

 Nishikawa 3 and has been used with caesium dichloriodide 4 

 and sodium nitrate. 5 



X W. L. Bragg, Proc. Eoy. Soc. A, 89, 468, 1914; W. H. Bragg, Phil. 

 Trans., A, 215, 253, 1915. 



2 Dolomite, which is often included in the calcite group, will not "be 

 discussed. 



3 S. Nishikawa, Tokyo Sugaku-Buturigakkwai Kizi (2) 8, 199, 1915. 



4 E. W. G. Wyckoff, J. Am. Chem. Soc, 42, 1100, 1920. 

 5 E. W. G. Wyckoff, Phys. Eev. (2), 16, 149, 1920. 



Am. Jour. Sci.— Fourth Series, Vol. L, No. 299.— November, 1920. 

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