180 yas Dana—Spodumene from North Carolina. 
combination of the occurring planes in this zone; in addition 
these planes, more especially those of the fundamental prism J, 
are usually pitted with little depressions which will be more 
particularly mentioned later. The crystals are often flattened 
Vieee ® SF es ee 
parallel to the clinodiagonal axis but nearly square forms show- 
ing only the prism J are occasionally observed. The terminal 
planes, when they may be said to exist at all, for the crystals 
are usually terminated very irregularly, are always rough, or 
striated. The only one of the terminal planes which is at all 
constant in occurrence is the hemi-pyramid r (321). The 
planes g (681), e (241), u (248), p (711) form an oblique zone, as 
shown in figures 1 and 2, and in the majority of the crystals 
the presence of the same zone is manifest, although no distinct 
planes are to be determined, the planes rounding uninterrupt- 
edly into each other and continuing the front edge (1/1) over 
the top of the crystals. This feature is shown in fig. 4 and 
also in figs. 5, 6, 7 which represent twin crystals. 
The twin crystals are common, probably more so than the 
simple crystals. The plane a (100) is uniformly the twinning 
plane and the twinning-axis is normal to it; it is also the com- 
position. plane. The twin crystals are usually nearly symmet- 
rical in form (see figs. 5, 6, 7), and the two halves are united in 
a sharp well-defined line, as proved by an examination with the 
polariscope. In the case of erystals not terminated, or with 
terminations too rough to show whether or not they are twins, 
the composite character is proved by the little depressions 0” 
the planes of the prism J, since they are inclined in the same 
direction both in front and behind (figs. 5 to 9). 
The observed planes are as follows :— 
