640 S. KOZU 



longest diameter, though the largest is 20 mm. or longer. Their 

 surfaces are not vitreous, or smooth owing to the presence of 

 pumiceous matrix and inclusions of olivine crystals with a few 

 magnetite grains. The olivine is in well-defined forms, as already 

 described. 



The roughness of the crystal faces and the twin striation upon 

 them made the use of the reflection-goniometer very difficult. 

 Even the cleavage piece used for the measurement of the facial 

 angle (001) : (010) did not give a satisfactory result, as the reflec- 

 tion on (010) was disturbed by the pericline twin striations. The 

 angle measured lies between 85 48' and 85 52'. Other approxi- 

 mate facial angles measured by the contact-goniometer are as 

 follows : 



/(no) : M(oio) 59° 30' 



y(2oi):P(ooi) 8i° 10' 



y(2oi) : M(oio) 90 50' 



y(2oi):/(no) 45 20' 



/(201) :P(ooi) : 42 



w(o2i):P(ooi) 46 40' 



From the above angles and the relation of the crystallographic 

 zones the crystal-faces which were identified have been determined 

 as follows: 



P(ooi), M(oio), T(iio), /(no), /(201), ;y(2oi), e(o2i), 

 w(o2i), ra(ii), 0(111), p(iii), an< i K24T). 



The faces P, M, y, T, /, 0, p, and n are always observed, of which 

 P. M, and y are the predominating faces. The face e is very rare, 

 and /, /, v, and m are only found in the tabular crystal parallel to 

 P(ooi). 



Some distinguishable crystal habits are formed by the pre- 

 dominance of different crystal-faces, as given below: 



First type: Prismatic, elongated along the axis a, with the 

 faces P, M, and y predominating, as seen in Fig. 6. 



Second type: Tabular, parallel to M, its elongation being along 

 the axis c, as seen in Fig. 7. 



