NO. 1867. CRYSTALLIZED VARISCITE FROM UTAH.— 8C HALLE R. 423 



CRYSTALLOGRAPHY. 



INTRODUCTION. 



The flat crystals are orthorhombic in their symmetry and simple 

 in their combination. The large tabular face is taken as the brachy- 

 pinacoid and the cliief forms noted, as shown in figure 2, are: h (010), 

 m (110), and e (012). In addition to these forms the macropinacoid 

 a (100) is sometimes present as a narrow face. Occasionally the 

 crystals are much longer and the prism faces more developed in 

 comparison with the macropinacoid. The com- 

 mon habit of the crystals is as shown in figure 2. 

 A better idea of the shape of the crystals can be 

 had from figure 1, on page 418, which shows a 

 variscite crj^stal so drawn as to bring the brachy- 

 pinacoid & (010) in front. The rectangular, tabular 

 shape of the crystals, due to the large development 

 of the braclwpinacoid, is there well shown. 



Several other forms are present on these crystals, 

 but they could not be determined. On crushing 

 some of the coarsely crystalhzed aggregate and 

 examining it under the microscope one occasionally 

 sees an acutely terminated crj^stal which has the 

 corners replaced by small faces, probably those of 

 the unit pyramid. 



In orienting the crystals of variscite three posi- 

 tions are available, depending on which pinacoid 

 the broad face is referred to. This broad face is 

 generally shghtly striated vertically. In conformity 

 with the analogous mineral scorodite, the striations 

 are taken as parallel to the c axis. Striated crystals 

 of scorodite have been described by several authors. 

 Thus, Kokscharow ^ states that the form (010) is 

 strongly striated vertically. Zimanyi ^ describes 

 scorodite crystals on which the prism d (120) is verti- 

 cally striated, and Lacroix ^ mentions vertical 

 striations on (120) and the two pinacoids (100) 

 and (010). He also describes scorodite crystals 

 sHghtly flattened parallel to either a (100) or h (010) and states 

 further that a rare phase of strengite is formed by plates flattened 

 parallel to a (100). 



The possibilities of the three available orientations will be dis- 

 cussed after the measurements of the variscite crystals are given. 



1 Kokscharow, N . Mineralogie Russlands, vol. 6, 1870, p. 309. 



' Zimanyi, K. Beitrage ziir Mineralogie der Komitate Gomor und Abanj-Torna. Fold. KozL, voL 

 35, 1905, p. 545. 



> Lacroix, A. Mineralogie de la France, vol. 4, 1910, p. 472. 



Fig. 2.— Variscite 

 CRYSTAL 6 {010}, m 

 •{110}, e {012}. 



