308 MINERALOGY. 



TrippTceite. — A copper arsenite from Chili, the composition of which 

 was determiued by A. Damour, and the crystallographic properties 

 by G. vom Eath. It is a quadratic mineral, the optical proof of which 

 was furnished by Des Cloizeaux. It was named for Dr. Paul Tripkie, 

 a mineralogist in Bonn, who was unfortunately killed shortly after he 

 had found this mineral, which he suspected to be new. 



Tysonite. — A mineral found by Messrs. Tyson and Wood, on Pike's 

 Peak. It was found by Prof. O. D. Allen and Mr. W. J. Comstock 

 to be a fluoride of the rare earths cerium lanthanum and didymium. 

 It is a hexagonal mineral of vitreous and wax-yellow color, and very 

 heavy. It was named from the finder. 



Urisite. — An hydrous iron sulphate, containing soda, described by A. 

 Frenzel. It has a citron or i)omegranate yellow color, and occurs in 

 rhombic crystals. It was obtained in the Caucasus. 



Urvolfjyite. — This is the same thing as the Herrengrundite described by 

 Brezina. This name was given by Szabo, but the lime which Brezina 

 found resulted from an intermixture of gypsum, Szabo considered to 

 be an essential constituent. 



Xantholite. — Another of Heddle's possibly new minerals. Found at Loch 

 Ness, Scotland. Like grenatite, but of different color. A poorly de- 

 termiued species. 



IMPORTANT STUDIES. 



It will be noticed that many of the new studies have consisted in the 

 continued application of the later developed optical methods to pre- 

 viously-determined species. This is because the ideas which constitute 

 a crystal have been changed, thus necessitating a reinvestigation of all 

 minerals. One sees no more in the new text books that a crystal is a 

 l)ody bounded by planes symmetrically arranged by forces of crystal- 

 lization. But a crystal is a body with a defined molecular structure, 

 possessing like elasticity in like directions. The planes which may or 

 may not bound such a substance are simply one of the features of this 

 molecular structure, in the same way as are the optical, electric, mag- 

 netic, thermal, and other properties. The isometric crystalline form 

 of a substance can be more perfectly established by the examination of 

 a pair of sections from an irregular fragment than from the outer form 

 of a developed geometrical form. Opaque substances only are investi- 

 gated in the same way as of old, and even these can be studied by thermal 

 methods. The degree of symmetry in crj^stals are considered as the 

 I)rominent features in geometrical study, and the crystalline axes, such 

 as are not assumed for simple convenience of calculation, are the nor- 

 mals to these planes, and not imaginery lines. These princiides, which 

 have much simplified the science in some directions and comi^licated it 

 in others, are not new developments, but progress worthy of note has been 

 made in the more general acceptation of the new system and its intro- 

 duction into elementary instruction. 



