Kraus and Cook — Ioclyrite from Tonopah. 215 



ently holohedral. The forms observed are c \ 0001 } , c'\ 0001 \ , 

 raj 1010 1, ^j 2021 1, and ^{2021}. Figure 4 shows these forms 

 in combination. 



Type 4. Due to the predominance of two parallel faces of 

 the prism, m{1010J, crystals of this type are also tabular. 

 They are, however, hemimorphic, as is clearly shown in figure 

 5. The figure shows a c_ombinatio_n of the following forms : 

 c{0001J, m{1010J, t{7073\, •{2021}, and i'{2021\. These 

 crystals are by no means as common as those of types 1 and 2. 



Type 5. Parallel grouping plays an important part in the 

 formation of crystals of this group. This is shown in figure 6. 

 These crystals are made up of several simple individuals which 

 possess, in general, a habit similar to that which is so charac- 

 teristic of crystals of type 2. Although they show hemimor- 

 phism, they are, nevertheless, more or less barrel-shaped, 

 resembling to a large extent the development so often observed 

 on crystals of corundum. The observed forms are cjOOOl}, 

 mjlOlOJ, i{2021\, and i'{2021\. These crystals are rather 

 common and are sometimes as much as 5 mm in length. 



Type 6. Crystals belonging to this group are more or less 

 carrot- or top-shaped. This is illustrated by figure 7. As is shown 

 by the illustration, these crystals are made np of a number of 

 individuals possessing a tabular development similar to that of 

 type 3 (figure 4). The crystals show the upper base c|000_l( 

 rather large and are terminated below by the pyramid i' \ 2021 \ , 

 thus giving the groups a decided hemimorphic development. 

 In many cases these crystals show a skeletal development in 

 that they are more or less hollow. In figure 7 we show the 

 general character of these crystals and also indicate the skeletal 

 development by figuring a depression in the upper base. In 

 some cases this depression does not extend far into the crystal, 

 while in other instances it extends almost the entire length of 

 the same. The bottom of this depression, which is usually 

 irregular in outline, but sometimes may be hexagonal, is a 

 plane surface, which from the reflections obtained on the goni- 

 ometer we know to be parallel with base CJ0001J. The sides 

 of the depression are usually characterized by parallel and 

 horizontal corrugations. These can be seen best in the crystal 

 fragments. The forms _obseiwecl on crystals of this type are 

 c{000r;, m-il010;, *{2021} 1 and * / J2021{. 



Type 7. Here belong contact twins with the pyramid 

 e {3031 \ acting as the twinning plane. The two individuals 

 are about equally developed and possess a tabular habit, as 

 shown in figure 8. This tabular habit is due to the predomi- 

 nance of two parallel faces of the prism m\ 1010 \ . These twins 

 are rather common. 



