2,2 NEW YORK STATE MUSEUM 



The Peekskill emery is a hard, dense rock of rather variable com- 

 position and dark gray to black color. It occurs in small lenses, 

 bands and irregular masses in the area of basic igneous rocks that 

 outcrops south and east of Peekskill. The emery bodies are found 

 mainly in the northern section of the area and apparently near the 

 contact of the igneous, or Cortland, series with the sedimentary 

 schists. They represent without much doubt segregations within 

 the intrusive mass similar to the titaniferous magnetites that occur 

 within the gabbros and anorthosites of the Adirondacks. The sur- 

 rounding sediments may have been absorbed more or less into the 

 igneous mass on its way to the surface, thereby contributing some 

 of the aluminum which has crystallized out in the form of corun- 

 dum and spinel. The intrusion took place after the deposition of 

 the Hudson River strata which are made up largely of argillaceous 

 materials. 



The emery is a mixture of corundum, spinel and magnetite, with 

 more or less of the silicate minerals that are found in the wall 

 rocks. The proportion of the oxids varies greatly. In some places 

 magnetite constitutes nearly the whole mass and such bodies have 

 been worked in the past for their iron, though not with much suc- 

 cess. Spinel (hercynite) is intimately associated with the mag- 

 netite, though its presence is seldom to be established without 

 microscopic examination, being in finely divided particles scarcely 

 distinguishable from the latter in the hand specimens. Its occur- 

 rence may account for the high aluminum percentages shown in 

 analyses of the magnetites, even in the absence of corundum. The 

 latter is a fluctuating constituent, constituting as much as 50 per cent 

 of the emery in places, but usually considerably less. It appears in 

 the form of thin prismatic crystals which are set off by reason of 

 their light color and their relatively large size from the magnetite 

 and spinel. The mines consist of open cuts on the outcrop of the 

 bodies, occasionally supplemented by a single underground level 

 reached through an adit. They have little permanent equipment, 

 b-^ing too small to warrant any considerable outlay for machinery ; 

 consequently there is a lack of stability and system to the opera- 

 tions. 



The present source of supply is mainly from one or two proper- 

 ties on the northern border of the Cortland area. The Keystone 

 Emery Mills and the Blue Corundum Mining Co. have been the 

 principal shippers of recent years. There are a number of mines 

 in the section north of Dickinson hill and south of the east-west 



