ALABAMA MICA DEPOSITS 27 



orable forms of more perfect crystallization at greater 

 depth, usually below water level. Masses however of 

 mica of A-structure, in Clay County, Alabama, have in 

 contradistinction, been taken out at a depth below water 

 level, in direct association with considerable amounts of 

 flat sheet mica of high grade. In close proximity to these 

 variable deposits, following the well defined strike of ap- 

 parently the same pegmatite leads, no A-form mica what- 

 ever occurs, and there has been recovered some of the 

 finest and largest muscovite ever found in the United 

 States, running in the lower entries of the mine up to 

 sizes approximating 12 by 18 inches, of smooth flat sheet, 

 almost wholly free from imperfections. 



By reason of its marked resistance to ordinary weath- 

 ering and resultant decomposition, mica is very generally 

 of surface occurrence along the outcrops of pegmatite, 

 enabling them to be readily traced up and developed. De- 

 composition of, or alteration in, mica crystals or blocks 

 on or near the surface, however, varies somewhat, being 

 governed by their hardness and associations. Thus open 

 and clay-stained blocks, are commonly found extending 

 to variable and often considerable depths under culti- 

 vated areas of long standing, while in or on outcrops of 

 quartz, of pegmatite aggregates, crystals not infrequently 

 occur, sound, unaltered, and free from imperfections, di- 

 rectly on the surface. 



PROPERTIES AND CHARACTERISTICS. 



In its application to the industries, mica, by reason of 

 its more or less perfect cleavage, flexibility, elasticity, 

 toughness, semi or perfect transparency, non-conductivity 

 of heat and of electricity, and comparative resistance to 

 decomposition, possesses qualities not shared by any oth- 

 er mineral product. The immense and constantly ex- 

 panding growth of the electrical industry has been largely 

 due to and dependent on the use of mica insulation, for 

 which mica is indispensable and has no adequate substi- 

 tute. Its necessary use in condensers, has recently been 

 the means of radical changes and large economies in wire- 

 less telegraphy. 



