FOEM SYSTEM OF THE WOLFRAMITE GROUP. 69 



it having cleaved off. The face of t{ 102} is much narrower than that 

 on figure 31. 



Crystal 25 (fig. 33) shows a rhombic crystal similar to those shown 

 in figures 7 and 13 (pp. 57, 59), witli the broad orthopinacoid a{100}, 

 replaced by numerous narrow alternating faces of a{100} and Z{210}, 

 those of Z{210} being much narrower than those of a{100}. The 

 form 7/{904} is also present. The drawing is, however, but a poor 

 representation of the true appearance of the crystal. Crystal No. 26 

 (fig. 34) shows the rhombic combination, a, b, t, modified by c{001} 

 and 77{ 904}. 



FORM SYSTEM OF THE WOLFRAMITE GROUP. 



CRITICAL STUDY OF FORMS. 



Before the monoclinic character of wolframite was determined it 

 was considered as orthorhombic, and it is therefore not possible to 

 tell which are the negative and which are the positive forms in the 

 earlier descriptions. The list of forms is fairly extensive, a total of 

 49 being recorded. Some of these forms will be briefly commented 

 on, as follows: 



${7.11.0} was described by Warren as new and the letter i assigned 

 to it. As, however, i had already been preempted by the form 

 {403}, the letter # is assigned to the form {7.11.0}. The measured 

 angle is given as follows: (7.11.0): (7.11.0) =74 51'. The calcu- 

 lated value is 75 16' and the calculated value for the simpler form 

 {580} is 74 16'. The differences between the angles measured and 

 the values calculated are, for {7.11.0} 25' and for {580} 35'. 

 Although the difference is slightly less for the more complex symbol, 

 the agreement is far from satisfactory. The correct symbol of the 

 form is therefore in doubt, and, though the indices would seem to 

 be possibly simpler than {7.11.0}, these indices are inserted in the 

 table of forms, but are marked with a (?) to indicate that the sym- 

 bols need verification. (See also p. 55.) 



w{021} was noted only by Descloizeaux and by Jeremejew. 

 Attention is called to the fact that {021} occupies almost exactly 

 the same position as c{001} in twin position. It is therefore possible 

 that a face of c{001} in twin position (as shown in fig. 35) was 

 measured and taken for (021). 



c(001) : (021)=60 01' (calculated). 

 c(001) : 2 (001)=60 02' (calculated; p. 62 



The difference between the two values is so small as to be immeasur- 

 able. It seems right, therefore, to regard the form w{021} as doubt- 

 ful and as at least needing verification before it can be accepted as 

 a definite form. 





