34 NEW YORK STATE MUSEUM 



The occurrence of graphitic quartzites has been shown by pros- 

 pecting to be quite common in the eastern section of the Adiron- 

 dacks, in Warren, Washington and Essex counties, and considerable 

 deposits occur also in the northwestern part in St Lawrence county. 

 The separate areas represent, apparently, the broken, eroded rem- 

 nants of once extensive beds which belong to a single formation. 

 They are interbedded with crystalline limestones, schists and gar- 

 netiferous gneisses that belong to the Grenville series of the early 

 Precambric. The stratigraphic position of the quartzites in the 

 bedded series has not been determined, owing to their greatly dis- 

 turbed and eroded condition. The quartzites and quartz schists 

 are hardened sandstones, and the graphite almost certainly is of 

 organic origin, derived from plant or animal remains included in 

 the rocks at the time of their deposition. The graphite content is 

 quite constant within the ^ same layers of a deposit, though it may 

 vary considerably in a direction at right angles to the bedding planes. 

 There is great variation in the graphite percentages in the different 

 occurrences, the richest deposits carrying around 8 or 10 per cent, 

 whereas the usual average is not over 2 or 3 per cent. Rock with 

 less than 5 per cent can not be considered as within the range of 

 economic utilization. There are other factors that have to be con- 

 sidered in addition to the graphite tenor, such as the size of flake, 

 the presence of other scaly minerals, and the degree of crushing 

 that is necessary to effect a separation of the graphite from the 

 gangue. Very rarely does a deposit possess all the requisites for 

 economic production ; in fact the American mine is the only one of 

 a number of enterprises to win a permanent success in the industry. 



One of the commoner difficulties in the way of utilizing the Adi- 

 rondack deposits pertains to the presence of more or less mica 

 which is disseminated usually through the quartzite in intimate asso- 

 ciation with the graphite. The particles are of approximately simi- 

 lar size, and being of the black variety (biotite) they may be readily 

 overlooked in the hand specimen or in the graphite concentrate. 

 The easiest method of detecting the mica and of estimating its rela- 

 tive proportion to the graphite is to examine the material under the 

 microscope when the former can be readily distinguished by its 

 translucency. The results of previous experience in mill treatment 

 with the use of buddies, concentrating tables, pneumatic jigs and 

 screens have shown that the mica can not be eliminated by such 

 methods. There is a possibility that this difficulty may he overcome 

 through the use of an electrostatic process, such as has been per- 

 fected in recent years and applied with some success lo the metallic 



