.MINKKAI.Oiili'AI. Nnl I-; 



-ANliEKSiiN. 



•J8 



ill some cases modiBed by small faces of >• (111) at tlie apex (Hg. 1), or 

 tnincaied bv a rough and uneven basal pinacoid. Most, of tlie crystals 

 are simple, but twinniusf on tlie usual law is exempllHed (tig. 2). Tlie 

 crystals are small, the largest being about 15 cm. in length jiml jet black 

 ill colour. Of t/he forms present /.• (340) is a fairly large face, the other 

 prisms a (100) and di (110) being narrow ; there are indications of the 

 prism (130) for which the measured angle <^ was 18° 6' and 19" 3' 

 (calculated 18° 2(5'), but, as the j)risnis generally are striated and the 

 signals poor, this is not included in the list of forms. The pyramid 

 .< (Ill) is small when present, but the faces are brilliant and give good 

 signals. 



Forms and Angles : 



Tingha (Y), N.S.Wales. 



(PI. vii., figs. 4, 5.) 



A small collection of crystallised cassiterite, believed to be from the 

 Tingha disti-ict, exhibits an unusual habit. Practically all the crystals 

 are composed of three portions, one of which is relatively large, doubly 

 terminated and cairies the two smaller portions twinned to it on two 

 opposite faces of c (101) ; the composite crystal is inclined to be tabular 

 in the plane containing the twin axes, and in shape is not unlike the 

 letter S. The ci-ystals are all small, the figured specimen measuring 

 about 8 ram. in greatest length, and their unifoimity in shape and 

 development is very striking. Two opposite faces of u (100) are the 

 largest planes on the crystals; one of these, shown in front in the figures, 

 is smooth and biilliant and gives a good signal, although it is a composite 

 face formed by coplanar portions of the three twinneil segments. The a 



