GEOLOGY OF GRAVES MOUNTAIN 209 



Microscopically, thin sections of the massive quartzite show a fine 

 granular mosaic of closely interlocking angular quartz, shreds of muscovite, 

 and some cyanite in large crj^stals. Neither biotite nor feldspar was iden- 

 tified in any of- the thin sections of either phase of the rock or in any of 

 the hand specimens. Quartz greatly predominates. Rutile is present in 

 every thin section examined, usually as separate grains and as inclusions 

 in the quartz and cj^anite. Most of the quartz anhedra are approximately 

 of the same size but frequently occasional larger individuals occur which 

 show strain shadows and peripheral granulation. The quartz contains 

 liquid and solid inclusions, dustlike particles of an indeterminate character 

 and rutile being the commonest of the solid forms. Alteration of the indi- 

 vidual minerals, including lazulite,as shown under the microscope is described 

 below separatel^r under each mineral. 



MINERALOGY. 



The mineral association at the Georgia locality is somewhat similar 

 to that at Clubb and Crowder Mountains, North Carolina. The minerals 

 include pyrophyllite, lazulite, rutile, cyanite, and hematite, and are de- 

 scribed below in the order named. 



Pyrophyllite. Pyropliyilite, a hydrous aluminum silicate correspond- 

 ing to the formula H2Al2Si40i2, occurs at Graves Mountain, Georgia, in 

 stellate or radiate aggregates, a less frequent occurrence of the mineral 

 than in foliated or compact massive forms. The radiate form of occurrence 

 has been noted at several localities in the United States,* chief among 

 which are the Chesterfield district in South Carolina; Graves Mountain, 

 Lincoln County, Georgia; Cottonstone Mountain, Mecklenburg County, 

 North Carolina; and the Kellogg lead mine, near Little Rock, Arkansas. 

 Genthf reports the occurrence of lazulite and cyanite with pyrophyllite 

 at the South Carolina localitj^, a similar association to that of Gaston 

 County, North Carolina, and Lincoln County, Georgia. 



Very few good exposures of pyrophyllite were observed on Graves 

 Mountain. The best and largest one occurs some distance up the north- 

 west slope on either side of the road which leads on top of the mountain 

 from the northwest side. Here the mineral is exposed as a solid mass of 

 several feet in thickness in greatly weathered and etched low cliffs. It 

 forms fibrous radiate aggregates averaging about a quarter of an inch in 

 diameter, partially discolored a light dirty brown from infiltrating iron 



* Dana, E.g., A System of Mineralogy, 1900, 6th ed., p. 692. 

 t Genth, F. A., Amer. Journ. Sci., 1854, vol. 18, p. 410. 



