GENERAL CHARACTER OF THE CRYSTALS. 



41 



different crystals being well shown by the irregular lines crossing 

 the prism zone normal to the vertical striations (fig. 2). The distri- 

 bution of the dome faces on several of the parallel groupings joined by 

 the a (100) face conclusive- 

 ly demonstrates that the 

 crystals are not twinned. 



Well-developed crys- 

 tals are abundant, but 

 many crystals are rounded 

 and curved either in a 

 single zone or throughout. 

 The curving of the sur- 

 faces in a single zone is 

 generally due to the 

 marked development of 

 the striations in the prism 

 zone. (See fig. 9, p. 59.) 

 The curving of the faces 

 over an entire crystal is 

 due to the nearly parallel 

 grouping of a number of crystals, each one deviating successively a 

 little more from parallelism with the original unit. 



The various forms of occurrence of ferberite found on the specimens 

 examined may conveniently be summarized as follows : 



1, Massive. 



2, Bladed, indistinctly crystallized. 



3, Distinct individual crystals. 



a, Single well-formed crystals (Pis. 

 VII, VIII, XI, and XII, 

 and text figs. 3-34). 

 6, Twinned crystals (PL VIII,A, and 

 text figs. 14, 15, 17, and 18). 

 c, Crystals grouped in parallel po- 

 sition (Pis. IX and X). 

 ' (1), Composition face a(100) 



(fig. 1). 

 (2), Composition face c(001) 



(fig. 2). 



<f, Rounded crystals or groups of 

 crystals. 



FIGUBE 1. A , Orthographic projection of crystals with similar 

 combinations in parallel grouping, joined by the o(100) face; 

 B, Orthographic projection of two crystals with dissimilar 

 combinations. The cleavage parallel to 6(OlO) in many crys- 

 tals terminates one side. Forms: c<001>, 6{010>, o<100>, 



FIGURE 2. Superposed crystals, joined by 

 the c(001) faces. The line of demarcation 

 is normal to the vertical striations on the 

 large o(100) faces. 



SIZE. 



In size the crystals vary considera- 

 bly. The largest seen were about 

 1.5 centimeters long (b axis), half as high (c axis), and about 4" milli- 

 meters thick (a axis). The general average would be about 5 to 10 milli- 

 meters long, 2 to 5 millimeters high, and 1 to 3 millimeters thick. On 



