CRYSTALLOBLASTIC ORDER AND MINERALS 



503 



Microscopic. — All the quartz is secondary. It often occurs in long thin 

 blades and in thin plates parallel to the schistosity. Sericite has given place 

 largely to muscovite. There is extreme parallelism of the constituents which 

 are clear and free from indications of strain. The metamorphic (secondary) 

 minerals are as abundant in the pebbles as in the paste. Recrystallization in 

 pebbles and paste is at a maximum. 



STUDY OF THE METACRYSTS 



Many of the fine-grained schists of the last three stages contain 

 metacrysts, or pseudophenocrysts, of ilmenite, biotite, garnet, and 





Fig. I. — Crystal of ilmenite sand- 

 wiched between layers of secondary 

 quartz. 15 diameters. 



Fig. 2. — Metacrysts of biotite and 

 ilmenite in a rock with poor flow cleav- 

 age. (See Fig. 3.) 15 diameters. 



ottrelite, named in order of decreasing frequency. The same 

 minerals are found in some of the coarser rocks, but in these 

 they are no longer conspicuous for their relatively large size. 

 The relations of these four minerals to one another and to the 

 schistosity in the different stages of metamorphism will be de- 

 scribed herein in greater detail than was possible in the earlier 

 paper on this subject.^ 



Ilmenite. — In rocks of Stage B metacrysts of ilmenite occur as 

 tabular crystals, thin or thick as the case may be (see Figs, i, 2, 



' F. H. Lahee, op. cit. 



