MINERAL RESOURCES OF THE STATE OF NEW YORK I49 



Ries, H. & Eckel, E. C. Lime and Cement Industries of New York. N. Y. 



State Mus. Bui. 44, 1901 

 Vanuxem, Lardner. Geology of New York. Report on Third District, 1842 



MICA 



The production of mica has never attained the basis of a settled 

 industry in this State, although small quantities are extracted from 

 time to time in an experimental way as a secondary product in the 

 mining of other minerals. The occurrences illustrate the general 

 types of deposits which have commercial importance elsewhere as 

 sources of mica and are distributed over the two great crystalline 

 rock areas of the Adirondacks and the southeastern Highlands, 

 being found in Orange, Putnam and Westchester counties in the 

 Highlands, and in Saratoga, Essex, St Lawrence, Jefferson, Herkimer 

 and other counties in the northern area. It is the purpose of the 

 present article to give some particulars regarding the character and 

 economic features of the deposits which hitherto have received little 

 more than casual attention. 



Mica is a general term for a group of minerals, of which three 

 varieties find commercial use. These include muscovite, biotite and 

 phlogopite. Muscovite is often called white mica, in allusion to 

 its transparent quality, but it is not necessarily light or highly 

 transparent, though the best commercial kinds are thus character- 

 ized. Some muscovite from the Adirondack pegmatites has a 

 smoky gray color, nearly as dark as some examples of biotite. Chem- 

 ically it contains potassiimi and soditim as basic elements, and is 

 therefore an alkali variety. Biotite, as a rule, has a dark brown to 

 nearly blaick color, but occasionally is sufficiently light to be trans- 

 parent in thin sheets. Iron is present in considerable amounts and 

 with the dark color renders it unsuitable for many purposes. Phlogo- 

 pite is a magnesian variety, containing no iron, but less transparent 

 usually than the best muscovite. Its color is amber or yellow, 

 sometimes red or of a greenish tinge. It is employed for the same 

 purposes as muscovite, but seems to be even preferred to the latter 

 in electrical work. The distinction of the different varieties of mica 

 when not apparent from outward appearance requires the use of a 

 polarizing microscope, supplemented possibly by chemical tests to 

 determine the nature of the basic elements. 



Muscovite and biotite are allied in their occurrence, both being 

 important ingredients of the crystalline silicate rocks such as granite, 

 and many gneisses and schists. Typical granite contains both 



