52 



COLORADO FERBERITE AND THE WOLFRAMITE SERIES. 



FORMS PREVIOUSLY DESCRIBED. 



COMMON FORMS. 



The common forms merit only a brief description, as their relative 

 development and occurrence can well be seen by studying the draw- 

 ings illustrating the different combinations and habits. 



In the prism zone the orthopinacoid a {100} is always strongly 

 striated vertically. These striations are not shown in the crystal 

 drawings. The orthopinacoid is often replaced by vicinal forms sev- 

 eral degrees from the true position of a{100}. On other crystals 

 the faces of a {100} are very close to their true position of 90 00'. 

 No connection could be traced between the presence of vicinal forms 

 replacing a{100} and the presence of new or rare prisms, as the 

 following table shows : 



Measurements of a{100} and list of associated prisms. 



The common prisms Z{210} and m{110} are striated on some 

 crystals and free from any striae on others, those without striae 

 yielding good and distinct reflections. 



The base c{001} is generally rounded in the zone {001}:{100}, 

 commonly giving several reflections, the extreme ones on some crys- 

 tals being several degrees apart. 



The faces of /{Oil}, generally small, all gave good and distinct 

 signals; those of {102} were generally distinct, although on a few 

 crystals they were somewhat blurred. 



The pyramids are generally so small that the reflections from their 

 faces are faint. The striations on J{112} cause the large faces of 

 this form to yield indistinct and blurred signals. The striations are 

 shown in figure 28 (p. 67). 



