68 



mica plainly is seen to be of the same origin as the preceding 

 type. All the crystals are rather rich in faces ; the size varies 



very much ; most crystals are 

 only a few millimetres , but a 

 single crystal reaches to a size 

 of 25 mm. 



Combination : è {OIO}, (Z{l 40} , 

 б{120}, i¥{no},A{210}, «;{30l}, 

 P{lOl}, с{001},я{012}, e{02l}, 

 /•{041}, o{lll}, .•{121},Ä;{411}, 

 £{43l}, л;{211}, ш{б21}; the 

 three last mentioned forms are 

 not found in all the crystals, and 

 are always rather small; ш(б21} 

 has not before been found in the 

 ilvaite; it is determined by lying 

 in the zone (411:210), and by 

 the angles : 



Fig. 14. Ilvaite, type XIII. 



— — Ç-, — . 



„ . . Number of Calculated 



variations measu,.ei,ients value 



ш:Д = (621):(210)=1Ь°472' 14°14'— 15°55' 2 14=57V2' 



The prismatic zone is always very highly striated, and gives 

 a very great number of reflexes, which is also the case with 

 that piece of the zone of brachydomes lying between (012) and 

 (012); ciOOl), which is always very long and narrow, is trans- 

 versely striated by being combined with the two mentioned faces. 

 Otherwise the crystals are well developed with bright faces, 

 which is, however, only the case to a smaller degree in the 

 larger crystals. 



Type XIV. 



Of this form we have an exceedingly rich material, almost 

 equal to that of type 1. The crystals are generally larger than 

 in this latter type, as a rule between 5 and 20 mm. 



