Cyanite from a Nexo Locality. 197 



rocks are found within the area, and it is distant about 15 

 miles from the exposed western margin of the granite and 

 granite-gneiss belt. From the composition and texture of the 

 schists it is inferred they were derived from original siliceous 

 and argillaceous sediments under anamorphic«conditions. 



The principal rock type is a thinly foliated quartz-sericite 

 schist of light color when fresh and of medium coarse grain. 

 It is composed of quartz and sericite as essential minerals, 

 with occasional grains of rutile and other accessory minerals as 

 microscopic inclusions. Thin sections show granulation and 

 optical disturbance of the quartz, the former (granulation) 

 being pronounced in the hand specimens. 



The second rock type is a cyanite schist of variable texture 

 according to whether quartz or cyanite predominates. Some 

 specimens show a fine-granular nearly white rock composed 

 almost entirely of sugary quartz, with occasional cyanite and 

 sericite. The other extreme is represented by a coarse aggre- 

 gate of greenish cyanite in flat prismatic individuals measuring 

 2 inches long by \ inch wide, and containing but little quartz. 

 Between these two extremes many gradations are traceable. 

 The principal minerals are quartz, cyanite, and sericite, with a 

 goodly sprinkling of rutile in places. Under the microscope 

 the effects of dynamo-metamorphism are shown in granulation, 

 fractures, and optical disturbance of the quartz. Cyanite 

 occurs in prismatic form having good cleavage development 

 parallel to the vertical axis, and contains some inclusions. It 

 is distributed irregularly through the rock and at times forms 

 the dominant mineral, ranging in size up to 2 inches long and 

 from green and blue to colorless. Rutile as grains and crys- 

 tals occurs with few exceptions in the substance of both 

 cyanite and quartz. Black tourmaline and garnet are noted in 

 places. 



Untile. 



The principal occurrence of rutile is in the cyanite schist 

 although occasional grains are observed as microscopic inclu- 

 sions in the quartz-sericite schist. The rutile is freqxiently 

 observed megascopically as minute grains in the hard rock 

 and in the sands derived from the decay of the schists. It is 

 red to reddish brown in color, very faintly pleochroic, and the 

 larger grains sometimes show cleavage. It is quite generally 

 fresh and very seldom shows incipient alteration peripherally 

 to leucoxene. It is associated with both quartz and cyanite, 

 more often with the latter, in euhedral and anhedral crystals, 

 single and twinned, and sometimes in aggregates. In several 

 thin sections the rutile appeared to be as abundant in the 

 quartz as in the cyanite. 



