﻿210 W. E. Hidden — Contributions to Mineralogy. 



3. Twin crystal of Molybdenite. 



The crystal here figured was brought to my attention by Mr. 

 C. S. Bement, who was the first to identify its twinned struc- 

 ture. It was found near Renfrew, Canada, along with other 

 remarkable crystals, some of which weighed nearly a pound. 

 One measured 3f X2-Jx2 inches in thickness, while another, a 

 thick hexagonal prism, was 4 inches long. My own measure- 

 9 ments on this crystal and on several 



others from the same locality (made with 

 hand goniometer) give the angle of the 

 pyramid on the base as 108°, but this 

 value at best is only approximate. These 

 crystals and the method of twinning here 

 figured seem to prove that molybdenite 

 should be referred to the hexagonal sys- 

 tem. Some few of the crystals suggest that the species may 

 possibly be hemimorphic like greenockite, but this cannot be 

 positively determined at present with the material at hand. 



4. On the Phenaeite from Florissant ^ El Paso County ', Colorado. 



Since the original announcement of this locality,* by the 

 writer, many additional crystals have been found by Mr. 

 Hiestand and the best of them were sent by me to Professor Des 

 Cloizeaux, at Paris, who has very kindly examined them. I 

 here give substantially his results as communicated to me in a 

 letter dated Feb. 4, 1886. 



"I send a drawing of the two most remarkable of your crystals. 

 One is a projection parallel to the base, offering an opportunity 

 to study the new face z and the proportional development of the 

 other occurring faces (fig. 1). The other is a perspective view 

 of a very small but highly modified (abnormally) crystal, 

 placed so as to show its most interesting forms" (fig. 2). The 

 planes found by Des Cloizeaux on these interesting crystals are 

 here given in his symbols, Miller's and Dana's, i. e. — 



e 2 (211, i); d l (Oil, i-2); k (312, i-%=b* d' d^); p (100, R); b l (Oil, -£); & 

 (122, -1); e l (111, -2); d 2 (021, -l 3 ): z (32l, \ % =$ $V) new; w(211, £ 3 , 

 =$d'V)\ h 2 (021, f-2); 2/(311, %-% ~$ d'V). 



Des Cloizeaux's calculated and observed angles (the latter in 

 parentheses) on these Colorado crystals are as follows : 



d 1 w adj. = 134° 15' (133° 50'approx.); d l z over w=123° 0'; d* V over w= 

 107° 52'; w z adj. =168° 45' (168° 50'); & 1 V over 0=144° 2' (144°); e* d* 



adj.=rl47° 51' (148 approx.); e z w over d* 122° 30' (123°); e 2 eWo^° 40'; e 2 

 * Vol. xxix, March, 1885, p. 249. 



