Blasdale.] 



Contribution to Mineralogy. 



341 



then easily shown to be lacking in definite crystallographic planes. 

 Many of these extinguished light parallel to their longest axis, but 

 others gave extinction angles of as much as 4 . The specific 

 gravity of some of the separated crystals was found to be 3 986. 

 The composition of this mineral, as shown by the analysis reported 

 in Table V, is clearly that of tremolite. It presents no unusual 

 features except the rather high percentage of lime and combined 

 water. 



CHLORITE. 



As previously noted, chlorite is a common associate of the 

 actinolite. Aside from its occurrence in the actinolite boulders, it 

 fills lenticular cavities and veins in the schist; its occurrence in 

 relatively large masses in the glaucophane rock has already been 

 alluded to. Material from the latter source only was examined. 

 It here assumes the form of a scaly-grained dense mass composed 

 of comparatively thick groups of cleavage flakes, the masses being 

 disposed without common orientation. The maximum surface 

 presented by these flakes did not exceed a square centimeter. In 

 some cases the mass parted in such a manner as to give rise to 

 more or less conchoidal surfaces. Crystallographic planes were 

 entirely absent. The cleavage flakes were comparatively trans- 

 parent, were of a yellow-green to olive-green color, though on 

 exposed portions red stains due to oxidation were very apparent. 

 They extinguished light like an isotropic medium. The specific 

 gravity of a portion weighing about twenty-five grams was found 

 to be 2.792. 



Portions from the interior of the mass and as free from oxida- 

 tion as could be obtained were used for the analysis reported in 

 Table V. The high percentage of silica and the other features of 

 the analysis at once show that it is prochlorite. It may be com- 

 pared with a specimen of that mineral analyzed by Vuylsteke, 

 which is reported in the fifth column of the table. 



TALC. 



Talc forms white or apple-green masses filling the interstices 

 between the actinolite crystals and is occasionally found in com- 



