Genth and Penfield — Contributions to Mineralogy. 199 



Akt. XXI Y. — Contributions to Mineralogy, No. 49 ; by F. A. 

 Genth, with Crystallographic Notes, by S. L. Penfield. 



In the following paper we give the results of the examina- 

 tion of some superior specimens of the very interesting ferric 

 sulphates from Mina de la Compania near Sierra Gorda in the 

 Province of Tocapilla, about 125 miles interior from Antofa- 

 gasta, Chili. They were recently brought from this locality 

 by Prof. Henry A. Ward, and are now in the cabinet of Mr. 

 Clarence S. Bement of Philadelphia, who very kindly placed 

 them in our hands for investigation. 



1. Amarantite. A. Frenzel.* 



The crystallization is triclinic, confirming the determination 

 made by optical tests on cleavage fragments by E. A. Wiilfing.f 

 The habit of the crystals, many of which are doubly termi- 

 nated, is slender prismatic, the vertical zone being composed 

 principally of the pinacoids a and b, 

 while the ends are modified by a 

 number of brilliant faces. Individ- 

 ual crystals are frequently 10 mm long 

 and l mm in diameter ; some of them 

 have a nearly square cross section, fig. 

 1, others are flattened parallel to the 

 pinacoid a, fig. 2. The forms ob- 

 served are, 



a, 100, i-i d, Oil, \-i' x, 10], — 1-t 



&, 010, i-X e, 011, \-\ p, 111,-1 



c, 001, f, 021, 2-2 o, 111, 1' 



M, 110, I h, 012, i-i n, 121,-2-5'. 



The following measurements were chosen as fundamental : 



c~a, 001*100 

 c*&, 001 a 010 

 CaC, 001*011 



88° 53' 

 84° 16' 

 31° 25' 



a~p, 100*111 

 a*e, 100*011 



57° 48' 

 92° 48' 



from which the following relations are calculated : 



a = 95°38'16" 0= 90° 23' 42" y = 97°13'4" 



a: l: c = 0-76915: 1 : 0-57383 



In addition to the above the following are some of the im- 

 portant measurements which were made : 



* Tschermak's Mittheilungen, ix, p. 398, 1888. 

 f Tschermak's Mittheilungen, ix, p. 402, 1888. 



