ALABAMA MICA DEPOSITS 25 



pegmatites, which are formations similar to granite in 

 chemical and in mineral composition but coarser in tex- 

 ture, their aggregate, made up of quartz, feldspar, and 

 mica ; varying widely in the relative percentages of these 

 constituent elements, as well as in the coarseness or 

 fineness of their combination. 



In the zone of weathering or within the limits of sur- 

 face decomposition, the feldspar in the pegmatites has 

 been in many localities either wholly or partially kaolin- 

 ized. 



The surrounding rocks, mainly of igneous and of meta- 

 morphic origin and probably of Archean age, are largely 

 made up of the constituent elements; mica, garnet, cya- 

 nite, and hornblende, being commonly granite gneisses 

 and schists, with occasional accompaniment or associa- 

 tion also of the soapstones and serpentines. 



The comparative regularity of the structural features 

 of the enclosing gneisses and schists, to which in large 

 measure the pegmatite lenses or bodies lie in conformity, 

 tends to render them also more or less persistent in 

 length along the strike, and often to considerable depth 

 on the dip, although presenting wide irregularities in 

 shape and form and variable in section as to width ; tap- 

 ering, widening and frequently as lenticular bodies over- 

 lapping. It is not uncommon to find them however as 

 distinctly cross formations. 



In the hornblendic areas, occurring at the extreme 

 southwestern end of the Alabama mica field, the pegma- 

 tites are uniformly made up of a quartz and feldspar ag- 

 gregate in small fragments or particles frequently car- 

 rying good flat muscovite mica of high grade, but gen- 

 erally speaking in sizes too small to be worth recovering, 

 the mica occurring largely in the kaolinized feldspars. 



Generally speaking, the irregular masses, lenses, 

 streaks, and bodies, of pegmatite occurring in Alabama, 

 present extreme variations in thickness, ranging from 

 a few inches to fifty feet or more. 



The quartz of the segregations is massive, usually 

 granular, frequently crystalline, and uniformly persis- 

 tent throughout the mass. Feldspar, usually either orth- 



