A. J. JToses — Crystallization of Luzonite. 277 



Art. XXX. — The Crystallization of Luzonite ; and other 

 Crystallographic Studies ; by Alfred J. Moses. 



1. The Crystallization of Tuzonite. 



The reddish bronze, fine-grained variety of Cu 3 AsS 4 which 

 is found in the copper veins of Mancayan, Luzon Island in 

 the Phillipines, has been generally accepted as dimorphous 

 with enargite, but the minute crystals, " tiny individuals of 

 unrecognizable form,"* observed in the cavities growing from 

 the granular mass have not been measured but rather referred 

 to as u indistinct, uneven, striated crystals not rhombic but 

 monoclinic or even tri clinic. "f 



Recently Mr. Maurice Goodman, senior field assistant in the 

 Bureau of Mines, Manila, collected a number of luzonite speci- 

 mens showing these crystals in cavities, from which I selected 

 and measured the crystals here described. 



Crystals JVo. 1 and JVo. 2. — A mass of typical luzonite, free 

 from all visible columnar blackish enargite, showed a number 

 of cavities the walls of which were crystallized ; that is, little 

 detached fragments of the walls under the microscope were 

 seen to be facetted by minute crystals which projected very 

 slightly and the faces of which could be traced down until 

 they merged in the bronze-colored mass. They were not 

 implanted on or enclosed in the mass, but distinctly suggested 

 that the mass on solidifying formed little facets such as form 

 on the cooling of a fused mass of pyromorphite. It is curious and 

 probably of genetic significance, that the terminal planes of these 

 crystals are decidedly lighter in color and of less brilliant luster 

 thau the side planes, the latter suggesting the dark gray of 

 enargite or stibnite and the former a reddish steel-gray not 

 very different from the tint of the massive luzonite. In more 

 than one instance in which a fracture extended across a crystal 

 into the massive material it was impossible to see any difference 

 in the color or character of the surfaces. 



Two little crystals were mounted for measurement. No. 1, 

 shown in fig. 1, was only -J- to -J- mm in any direction, but was 

 attached to a fragment of the mass from which it had devel- 

 oped. Signals were obtained in the two-circle goniometer 

 from seven faces but were a little blurred. Crystal No. 2, 

 shown in fig. 2, was the largest crystal I observed as a cavity 

 wall facet, and its terminal face was approximately a rhomb of 

 l-|X-| mrj . It also yielded signals from seven faces and a series 

 of signals from a curved triangular surface. 



In both crystals the terminal faces were reddish steel-gray 

 and the vertical faces dark gray. Taking the terminal faces 



*Weisbach, Tscher. Min. Mitth., 1874,. 257. 

 fFrenzel, ibid., 1877, 303. 



