5 26 General Notes. [June, 



melsberg were made upon material containing cryolite as an im- 

 purity, it being impossible to separate cryolite from chiolite in 

 the massive state. Professor Von Jeremejew has examined the 

 crystals of chiolite and finds them to be tetragonal. 



Chodneffite is merely an impure chiolite, and must be stricken 

 from the list of minerals. 



-Rhodizite, an extremely rare mineral, occurring 

 in minute crystals upon some red tourmalines in the Ural moun- 

 tains, ttnd supposed to be a borate of lime, has been the subject 

 of two recent communications by Bertrand to the Mineralogical 

 Society of France. The crystals present the form of a dodeca- 

 hedron, modified generally by tetrahedral faces. Bertrand con- 

 cludes, from an examination of their optical properties, that the 

 crystals are to be considered pseudo-isometric, and are composed 

 of twelve elementary monoclinic crystals twinned symmetrically 

 around a point. He has been able, moreover, actually to separate 

 these elementary crystals by cleavage. The elementary crystal 

 of Rhodizite consists, he holds, of an oblique monoclinic prism 

 of 120°, of which the height is equal to the width, and of which 

 the obliquity is 54 44/. 



Crosby's Common Minerals and Rocks. — The twelfth num- 

 ber of the " Guides for Science Teaching," issued by the Boston 

 Society of Natural History for the use of teachers, has been pre- 

 pared by Mr. W. O. Crosby, whose contributions to the geol- 

 ogy and lithology of Massachusetts have been of great value. 

 It is entitled "Common Minerals and Rocks," and is an ele- 

 mentary sketch treated in a familiar way, admirably serving 

 the purpose intended. About twenty-five of the rock-forming 

 minerals are described, special stress being laid upon their acidic 

 or basic relations and their associations The triclinic feispars, 

 for example, are stated to occur with basic minerals, while ortho- 

 clase is acidic in its associations. The silicates are divided into 

 the two groups of basic and acidic; all species containing >^Y 

 per cent, or less of silica being classed as basic, while those con- 

 taining more than sixty per cent, of silica are acidic. The basic 

 silicates are dark colored and heavy, the acidic being light in 

 color and weight, and the two classes of silicates belong to dis- 



The little treatise is written from the lithologist's standpoint, 

 and the larger portion of it treats of the origin and physical 'in- 

 ferences of rocks. The author classifies rocks according to their 

 geological origin. 



Martite.— O. A. Derby 1 has examined a large number of 

 octahedral crystals of Martite from Brazil, and concludes thai 

 while a portion of them have resu.ted from the decomposition 



1 Am. Journ. Sc. and Arts, May, 1882, 373. 



