102 Canadian Record of Science. 



and obtain on a clinopinacoid an extinction of 35° with a 

 prism edge. It is, in fact, identical with the pyroxene 

 described by Professor Lewis^ as chromediopside. In it 

 (though rarely) small rounded enclosures of a greenisli 

 mineral aggregate much blackened with opacite. I regard 

 them as alteration products of a ferriferous olivine. This 

 diopside, at the exterior and along cracks, is often con- 

 verted into a minutely granular to fibrous mineral, which 

 gives a " dusty " aspect to that part of the crystal when 

 viewed with transmitted light, and a whitish-green one 

 with reflected light. This often terminates in a minutely 

 acicular fringe, piercing the original diopside. Its grains 

 occasionally are a little larger, showing a cleavage, dull 

 green in colour, fairly pleochroic, and having the extinction 

 of hornblende. A process of secondary change, as in 

 uralite, is no doubt indicated. Now and then a tiny film 

 of brown mica occurs in this part or even in a crack in 

 the diopside. 



It is this alteration product wdiich gives the mottled 

 aspect mentioned above as visible to the unaided eye, so 

 this is not indicative of a third important constituent in 

 the original rock. In one of the slices the mica just 

 named attains a larger size (about 0.03 inch across), has 

 a fairly idiomorphic (hexagonal prism) outline, and is not 

 restricted to the margin of the garnet. In this case it is 

 generally associated with calcite,^ which it tends to sur- 

 round, and that in one place encloses a radiating acicular 

 mineral (? a zeolite), in another the calcite, or some other 

 carbonate, is mixed with a serpentinous material. Distinct 

 granules of iron oxide are practically absent from the 

 slices, though here and there it may be indicated by some 

 opacite. I have not found spinel, or rutile, zircon, or 

 pseudobrookite. In fact, putting aside the diamonds, 



1 J.oc. cil., p. 21. 



2 l''ioiii Ihe facts I tliiiik it piobably of secondary origin. It reminds me sometimes 

 of tlie brown mica produced by contact metamori>liisni. 



