578 



Pigs. 1 and 2 show a tvpic.ti ■ -r< -i ; i : orthographic and 

 clinographic projection respectively. Fig. 3 is an ortho- 

 graphic projection on the plane containing the a and c axes. 

 Type II. 



Crystals of this type also are elongated in the direction 

 of the o axis, but instead of being tabular on the a pinacoid, 

 they are prismatic in habit, the cross section at right angles 

 to the b axis being more or less square. Two crystals were 

 measnr •■■!, Iioth possessing all of the following forms: — 

 a (100), <A (201), a (101), c (001), 6 (101), v (302), v (201), 

 m (110), w (120), h (221), I (023), /' (011), p (021), s (111), 

 k (221), u (223), R (241). 



Fig. 4 represents an orthographic projection— the crystal 

 being held with the baxis vertical and the a axis running 

 right and left. 



Types I and II are thus seen to have many points of 

 similarity, the forms being practically identical and the 

 faces having almost the same degree of development. 

 The predominant forms are a </> c 6 y v m ft I f p, which 

 are present on all the crystals measured. Of these 

 the a and c pinacoids possess by far the largest faces— a 

 being the larger of the two and invariably striated, while 

 c is perfectly smooth and gives excellent reflections. Con- 

 sidering the orthodome zone, «/» and show the greatest 

 development. <i> is always large and smooth, often 

 striated, >/ and v invariably so. «r occurs only on a few 

 crystals and is somewhat narrow but smooth. 



On all the crystals measured a negative orthodome is 

 present intermediate in position between c and 0. On one 

 crystal two readings for the angle between this face and 

 the a pin o-oid were obtained, viz., 74° 17' and 71° 50'. This 

 may be, therefore, a new face 4*0*13. Another crystal 

 gives readings 82° 06' and 82° SI' and may be another new- 

 face 106. On all the other crystals, the readings are very 



