Ahwitlc Bocks at Isle Cadieux, Que. 9 



The biotite is often in idiomorphic hexagonal-shaped 

 plates and is not obviously poikilitic, but under the micro- 

 scope occasional corroded inclusions of chrysolite, angite 

 (?) and monticellite are to be found. It is mnch more 

 strongly colored than the biotite of the main rock. 



The melilite shows the typical tabular development 

 and the plates may be as mnch as 5 mm. across. The 

 crystals are conspicuously zoned, the zones being marked 

 by a difference in birefringence. The center of the 

 crystal is usually isotropic, though occasionally it is 

 barely over the border and in the positive series. The 

 outer zones are plainly negative and increasingly so as 

 one passes toward the rim. (See Plate I (a).) Even 

 here, however, the birefringence is still very weak, much 

 less, for example, than that of apatite. The measured 

 index of the ordinary ray is somewhat variable, but is 

 close to 1.636. The melilite, like the biotite, contains cor- 

 roded inclusions of chrysolite and monticellite. 



The apatite is present in such amount and in such large 

 prisms as to raise it somewhat above the class of minor 

 constituents. It is characterized by its freshness, lack 

 of cleavage and high birefringence as compared with 

 melilite. 



The presence of relatively small amounts of chrysolite, 

 augite, and monticellite as corroded inclusions in biotite 

 and melilite has already been mentioned. An analysis of 

 the melilite-biotite rock is given in Table II under I. 



Fine-grained Alnoite. 



The fine-grained type that has been called minette- 

 like in the hand specimen occurs at the southern side of 

 the knoll as a dikelike intrusive in the main mass. It 

 consists essentially of chrysolite crystals, partly resorbed, 

 lying in a matrix of biotite and melilite with the usual 

 minor constituents of the principal type of which it is 

 merely a textural variant. Augite and monticellite are 

 practically if not entirely absent, a condition which was 

 noted in one specimen of the main mass. This fine- 

 grained type is considerably fresher than the coarser 

 facies usually is. 



