458 RECORD OF SCIENCE FOR 1887 AND 1888. 



trapezoliedial tetartoliedrai division like quartz, with the consequent 

 power of circular polarization, has been recently studied by A. Schmidt,^ 

 and later by H. Traube,-^ on the morphological side. The material ex- 

 amined wasfrom Mount Avala, near Belgrade, in Servia, and the crystals 

 have aflbrded a considerable number of new forms, especially among the 

 trapezohedrons. These trapezohedral pianos are largely developed, thus 

 exhibiting this character of the species. On the rhombohedral side the ^ 

 tetartohedral species, tourm aline,'' dolomite,"* and phenacite^ have been 

 studied by Eamsay, Becke, and Pentield, respectively. The tetartohe- 

 dral character of tourmaline was shown in 1871 by the Russian miner- 

 alogist, Jerofeieff, who published a long paper upon the Russian species. 

 This paper, however seems to have been for the most part overlooked 

 by later writers. Solly (1881) describes a crystal from Pierrepont, I^^ew 

 York, with tetartohedral development of planes, and Ramsay shows that 

 there is no question in regard to this point. The crystals examined by 

 him were from Ramfos and Snarum, in isTorway, and exhibited the tetar- 

 tohedral character in the distribution of the planes and the asymmetric 

 form of the etching figures. 



Becke's monograph upon dolomite is an important contribution to our 

 knowledge of that species, giving a number of new forms, chiefly of the 

 tetartohedral character, that is rhombohedrons of the third series, and 

 establishing the right or left handed character of all these planes, as has 

 not been attempted before. He also describes the vicinal planes, and 

 the various methods of twinning with a large number of figures. Other 

 crystals of dolomite, also exhibiting these tetartohedral forms have 

 been described by A. Sella in a paper upon crystals of the rare mag- 

 nesium fluoride, sellaite,^ named in honor of his father Quintino Sella. 



The phenacite crystals of Mount Autero, Colorado, are described and 

 figured by Penfleld; they are interesting since a tetartohedral form, 

 that is, a rhombohedron of the third series is often the predominating 

 form and terminates the crystals sometimes alone. An earlier account 

 of these crystals was given by Des Cloizeaux. A somewhat related sub- 

 ject is the crystallization of the two ruby silvers, pyrargyrite and prous- 

 tite, studied exhaustively on the historical side a few years ago by Reth- 

 wisch and now receiving new contributions from the original work of 

 Miers.' He decides upon slightly diflerent angles for the fundamental 

 rhombohedron from those of Rethwisch (viz, 71° 22' pyrargyrite, 72° 12' 

 proustite) and questions his conclusion as to the relation of this angle 

 to the composition. The study of the fine series of specimens in the 

 British Museum has enabled him to add upwards of twenty new forms 



'Zeitsclier. Kryst., vol. xiil, 433. 



-Ibid., vol. XIV, 563. 



^ Bibaiig Svensk. Vet. Ak. Haudl., vol. xii, p. 9. 



■1 Miu. petr. Mittb., vol. X, 93. 



'^Amer. Jouru. Sci., vol. xxxiii, 130, xxxvi, 320. 



f'Mem. Accad. Lincei, vol. iv,read November 13, 1887. 



'^ Mineralogical Magazine, 1888, vol, viif* p. 37. 



