7 4 T. HI KL 



those crystals, in which pyramids as well as base are prominent. 

 The face X, which is very common in the Omi crystals (see fig. 20), 

 has been observed only in two specimens from Mino. The etched 

 figures on /and y appear in some cases like pyramids. 



Prismatic faces are much striated. The commonest are M and /, 

 while m and g occur less frequently. The other faces (0, n, X and T) 



21 ÏÎ 



are scarcely recognisable. Besides, however, oo P — — and cc P — 



have been noticed, by Hahn and by Matthew respectively. 



The basal-pinacoid is found quite frequently on small crystals, 

 in which it is distinguished from cleavage, by its natural etched 

 figures. In large individuals, the base is seldom observed. 



The brachy-pinacoid is frequent ; whjle the macro-pinacoid, 

 though mentioned by Matthew as in Japanese crystals, has not yet 

 been observed in our collection. 



Different Types of Crystals. — Y. Kikuchi has subdivided the 

 crystals of topaz from Mino into 



(I) Domal type. 

 (II) Pyramidal type. 

 (Ill) Base-pyramidal type. 

 To these, I wish to add one more, the Tabular type (IV). The 

 four types are, however, connected by intermediate forms. 

 Type I. Domal type. (fig. 1-fig. 3). 

 Crystals more than 0.5 c. m. in width are mostly simple and 

 generally belong to this type. Smaller crystals, however, are richer 

 in faces, and rarely belong to this type. In this type /, M, and I 

 are predominant, while the pyramids u and o are subordinate. The 

 face o is less common than u. The macro-dome d is often observed, 

 but is generally small. The brachydomes X and y are rare. 

 Type II. Pyramidal type. (fig. 4-fig. 10). 



