334 W. G. WOOLNOUGH. 



it is calculated that C = -67536 (Dana -67232). A stereographic 

 projection on the plane (001) is given. 



For the sake of comparison, the elements for a monoclinic 

 crystal of the same form are given, taking the long axis vertical, 

 a : b : c = -69248 : 1 : -67900. fi= 124° 2' 

 The length along the pseudo-clinodiagonal a : 5 75 mm. 

 „ ,, pseudo-orthodiagonal b : 8*75 mm. 



,, ,, pseudo-vertical axis c : 13*5 mm. 



The stereographic projection of such a crystal on the plane (100) 

 is also given. The pseudo-monoclinic habit is produced by the 

 excessive development of two faces meeting in a polar edge and 

 the simultaneous development of the two faces parallel to them. 

 This form of distortion has not been noted by Dana, either for 

 cassiterite or the isomorphous form of Ti0 2 , rutile. Traces of 

 oscillatory combination with the prism [110] are indicated by a 

 striation parallel to the long edges. 



The pseudo-rhombic modification is of somewhat less interest than 

 the above since a similar distortion in the case of rutile is men- 

 tioned by Dana, though, so far, I have found no description of it 

 in the case of cassiterite. It is the result of excessive development 

 of alternate instead of adjacent faces at one of the poles of the 

 crystal, and of the parallel faces at the other pole. In this case 

 of the pseudo-rhombic crystal the faces of the pyramid of the second 

 order [101], those of the prism of the first order [110] and the 

 basal planes are noticeably developed, forming the pseudo-pyramid 

 and pseudo-pinacoidal faces in the distorted crystal. 



Levy and Lacroix (Les Mineraux des Roches, p. 119) describe 

 artificially formed hexagonal double oxide of tin and platinum 

 containing Sn 57*94 



Pt 22-48 



O 19-58 



100*00 

 and with a specific gravity of 6*70. The crystals form flat hexa- 

 gonal plates and are optically negative. As the cassiterite from 



