250 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE _ [VOL. XI 
In his experiments with the amphiboles, Daly” obtained well defined 
and uniform figures on the orthodome. They were usually of a regular 
triangular outline enclosed by three triangular faces. Occasionally 
however they were five-sided, the result of interpolation of pyramidal 
faces at the basal angles of the original pit. 
(e) Pits on the base. 
The conditions under which corrosion takes place on the basal 
pinacoid are quite similar to those under which it acts on the domes, 
and the resulting pits as will be seen from the drawing (Plate XXVI, fig. 32) 
are very similar, the only difference being that they are somewhat 
shorter. This shortening is suggestive when we compare the pits on 
the three principal faces in the ortho-diagonal zone, in which, beginning 
with the long, almost furrow-shaped figures on the pinacoid, the pits 
become shorter as we approach the base, where the length is at its 
minimum. 
After an exposure of 20 minutes to a 50% solution of commercial 
hydrofluoric acid at 100°, conditions under which the figures were de- 
veloped upon the domes, corrosion had so far progressed that the reflec- 
tion showed, as in a previous case, a nebulous band in which were a few 
more or less distinct spots. Further corrosion did not increase the 
distinctness of the reflections, on the contrary they appeared to become 
more and more hazy. 
6. ALKALINE CORROSION OF DIOPSIDE. 
In order to obtain pits by alkaline etching, specimens were exposed 
to the action of fused sodium hydrate, but unlike spodumene, diopside 
became rapidly over etched and covered by an opaque layer which no 
amount of washing or boiling with acids would remove. A solution of 
the same alkali proved ineffectual, but after an exposure of 15 seconds 
to fused calcium chloride, although the faces of the crystal frequently 
became clouded, minute but fairly clear and characteristic pits were 
produced upon the prisms. They were bounded by three sides, one 
short and straight, the others long and curved and approximately of 
the same length (Plate XXVI, fig. 33). They were enclosed by three tri- 
angular figure-faces, one of which had all three sides straight, while each 
of the others had one curved side, and were frequently arranged in 
vertical rows with their short sides lying parallel to a cleavage _trace. 
The only indications of etching upon the pinacoids at this stage 
were slight roughenings. 
12 op. cit., page 413. 
