34 
MUSEUM BULLETIN NO. 27. 
me try passing through the prism diagonally. Without dose inspection 
the crystals might easily be mistaken for diopside of normal prismatic 
habit, presenting the unit prism m(110); when measured and correctly 
oriented, however, it is seen that the apparent prism consists in reality 
of the four faces of the acute herni -pyramid A(331), the angle 331 A 331 
being 91°35'. The true prism zone has the forms a(100), f(310), 
i(130), b(010), and occasionally certain others, as cited in the list below ; 
Figure 11. Diopside, 
colourless crystal from the 
Montreal chrome pit; crystal 
with somewhat flat termina- 
tion, due to the equal de- 
velopment of the pyramidal 
forms t (Il2) s(Ill), »(221), 
and 2(331). 
Figure 12. Back view of 
Figure 11. 
but these are all very small as compared with A(331), the only one of any 
prominence being a(100), while b (010) appears only as a very narrow 
line-face truncating the edge (331:331). Othejr forms almost invariably 
present are z(021) f u(lll), x(221), s(lll), r(112), and the basal pina- 
coid. Figure 5 illustrates the habit and the relative development of the 
forms commonly exhibited by these crystals; it has been drawn with the 
edge (331:331) vertical in order to emphasize the prismatic appearance. 
One of the measured crystals having this habit is shown in orthographic 
projection in Figure 6. 
