510 Evans and Bancroft— Gedrite in Canada. 



amphibolite which stretches for about two miles along the 

 north shore of Fishtail Lake. This mass of amphibolite is 

 traversed in all directions by pegmatite veins. 



The amphibolite is- a dark basic variety, consisting largely 

 of anthophyllite and garnet associated with cordierite and 

 subordinate amounts of quartz, biotite, iron ore and rutile. 

 The anthophyllite is very abundant, occurring . in groups or 

 sheaves of long narrow individuals, often curved and without 

 proper crystallographic terminations. Under the microscope 

 the anthophyllite is seen to contain a few little inclusions of 

 black iron ore and of biotite. The mineral has a bright luster 

 and possesses that delicate clove-brown color which caused 

 Schumach, who first described this mineral, to give to it the 

 name anthophyllite. 



The mineral has a perfect cleavage parallel to the prism 

 (110) and also to the brachypinacoid (010). Two cleavage 

 fragments were selected and measured on a reflecting goni- 

 ometer. The average of four measurements gave the cleavage 

 angle as 54° 41'. In thin sections the mineral shows the loz- 

 enged-shaped cleavage traces characteristic of the hornblendes, 

 and in sections in the prismatic zone always presents a parallel 

 extinction. The mineral is negative and the pleochroism is as 

 follows .: 



X=pale yellow; Y == brownish yellow; Z=dove color or 

 gray. The absorption is Z^>Y^>X. 



Tbe cordierite occurs in colorless allotriomorphic individuals 

 which are slightly turbid when contrasted with the quartz 

 which they otherwise resemble. The mineral is biaxial and 

 displays itself no pleochroism, but shows in a striking manner 

 the little pleochroic halos so commonly found in this mineral 

 when it occurs as a constituent of metamorphic rocks. These 

 halos, which are quite numerous, change from deep yellow to 

 colorless as the section is rotated, each halo having in its cen- 

 ter a minute, colorless, rounded crystal with high index of 

 refraction and high double refraction. The cordierite also 

 shows in places the twin lamellae frequently observed in this 

 species and is occasionally somewhat altered, especially along 

 the cleavage lines, into the cryptocrystalline aggregate of some 

 micaceous mineral. It also occasionally contains the little 

 bundles of minute sillimanite crystals which occur so charac- 

 teristically as inclusions in cordierite. 



This is, so far as can be ascertained, the first occurrence of 

 cordierite which has been described from Canada. 



In order to obtain material for analysis a hand specimen of 

 the amphibolite was crushed sufficiently fine to pass through a 

 sieve of 70 meshes to the inch. To free the powdered material 



