Notes on Phlogopyte. 77 



alteration in the chemical and physical molecules of phlogopyte, is due to the 

 development of these inicrolites. Their negative chemical affinity towards hot 

 hydrochloric acid, indicates that these microlites are not magnetites (as was 

 supposed by many), but most likely menaccanite. 



The third group of enclosures consists of large colorless bodies, the form of 

 which is represented in fig. 15. They occur in lines, circles, and are more fre- 

 quent in biotite and muscovite. Zirkei figures a series of these strange en- 

 closures found in European mica, and give them the name crystallites. 



The examination of the phlogopyte basis in regard to its dichroism, was made 

 by the aid of the microscope and polariser. Rotating the latter, various shades 

 of yellowish-brown color could be seen. 



In the phlogopyte of Pope's Mills and Edwards, the %asal plane (o) is of a 

 bronze-brown color, similar to that of Edenville ; but in examining thin slices 

 or laminae of the first two localities, we will find that the coloring-matter is not 

 uniformly spread through the whole mass, but that it occurs in patches, formed 

 by bronze-red microlites — sometimes with an amethystine color. The phlogo- 

 pyte basis presents a greyish color, and seems to be in a changed condition, as 

 its flexibility is partly lost, having assumed a certain brittleness. It polarizes 

 in a faint bluish-white between the crossed Nicols. Laminae of moderate thick- 

 ness of Pope's Mills' phlogopyte show asterism. 



The coloring matter is due to microlites, which occur in the most variegated 

 outlines ; sometimes in form of a rhombohedron of about 120° and 60 , or in 

 hexagons of about 120°, but most of the microlites occur in very irregular and 

 most bizarre forms. Some assume a dendritic or arborescent shape ; some again 

 present a very irregular star. Another form of these microlites presents partly 

 straight outlines of a hexagonal habitus, whilst the other part is of the most 

 irregular shape. 



Zirkei, in his Mikrnscopische Ber chaff erheit der Mineralien mid Gesteine, 

 pictures similar microlites as belonging to mica specular iron ore, and which 

 have greatest resemblance with those of Pope's Mills. 



He describes, also, similar forms occurring in a mica, as hematite crystals, to 

 which the Pope's Mills' microlites may belong. Treated in cold acids for a 

 length of time, they do not show any alteration. 



The color of the hematite crystals is between the lightest shade of yellow and 

 brown-black, the color increasing with their thickness, or, as it is usually the 

 case, with the amount of laminae which are piled upon each other. In regard 

 to their position, no particular law seems to exist, but the writer has observed, 

 in some preparations from the above locality, that a number of the hexagonal 

 laminae were arranged in parallel position, the outlines of the hexagon running 

 in three directions. 



Zirkei mentions a similar occurrence of parallel-arranged hexagons in a mica 

 of Greenville. Under the polariscope, they polarize very distinctly in brownish- 

 red colors ; even those dark-colored, which appeared entirely opaque towards 

 reflected light, polarized in bright, dark-red hues. In regard to dichroism they 

 appear to be indifferent. 



A great number of the hematite laminae appeared to be filled up with fine, 

 needle-shaped microlites, arranged in a hexagonal manner, but sometimes only 

 one series of parallel lines is seen. They polarize with a strong light, but 

 showing no colors, resembling the above needle-shaped enclosures of the Canada 

 Mine. Their length was about 0.5 mm. 



These needle-shaped enclosures should not be taken for fissures or holes of 

 the hematite laminae, through which the white phlogopyte basis is visible. The 

 latter fissures appear frequently; sometimes as holes, straight lines or curves, 

 but only polarize similar to the phlogopyte basis, which they really present. 



