WHERRY AND LARSEN : RHODOCHROSITE AND SIDERITE 365 



TABLE 1 

 Angles Observed for Aurichalcite and the Corresponding Symbols of 



the Domes 



There are probably also rhombic pyramids elongated in the 

 direction of the vertical axis with very short intercepts on the 

 a axis. It is generally impossible to focus exactly these faces, 

 and as a result the a parameter cannot be calculated, nor the 

 symbols of the pyramidal faces. It sometimes happens that an 

 individual of aurichalcite is lying on one of these pyramidal 

 faces; the extinction angles and the observations in convergent 

 light become then valueless for the determination of the crystal 

 system. 



As to the optical properties of the aurichalcite it may gener- 

 ally be noticed that the extinction is straight along the (010) 

 (100) edge. The acute bisectrix is normal to the cleavage plate 

 (100), which exhibits mean birefringence. The crystal plates 

 are so small that it was impossible to measure the indices of re- 

 fraction and the other optical properties. 



MINERALOGY. — The indices of refraction of analyzed rhodo- 

 chrosite and siderite. 1 Edgar T. Wherry, National Museum, 

 and Esper S. Larsen, Geological Survey. 



Rhodochrosite. The beautiful, transparent, crystallized rho- 

 dochrosite from the John Reed Mine, Alicante, Lake County, 

 Colo., has been described by Dr. G. F. Kunz 2 who gave the FeO 



1 Published with permission of the Secretary of the Smithsonian Institution 

 and the Director of the U. S. Geological Survey. 



2 Am. Journ. Sci., (3) 34: 477. 1887. 



