THE ADIRONDACK MOUNTAINS 85 



which often occurs as good, very symmetrical crystals with twelve 

 or twenty-four faces or a combination of the two. Hardness, 

 greater than that of quartz or flint; color, red to reddish brown; 

 very brittle ; and only imperfect cleavage. Almandite is a siHcate of 

 aluminum and iron. 



Garnet occurs as an accessory mineral in many Adirondack for- 

 mations. In some phases of the anorthosite, syenite-granite and 

 gabbro, it is often clearly visible to the naked eye. Some of the 

 Grenville gneisses are rich in garnets, individual crystalline masses 

 frequently attaining diameters from an inch to a foot or more in 

 certain hornblende gneisses as, for example, at the garnet mines near 

 North Creek and at Thirteenth lake in Warren county. 



Graphite, Often called " black lead." Seldom appears as good 

 crystals, but nearly always as thin, shiny-black, flexible flakes with 

 one almost perfect cleavage. It is opaque, easily scratched by the 

 finger nail, and leaves a black mark on paper. Composition, pure 

 carbon. 



Certain of the Grenville gneisses, schists and quartzites, and most 

 of the limestone contain graphite in clearly visible flakes in amounts 

 up to 10 or 12 per cent. Rarely, small veins of graphite have been 

 found. Graphite-rich schists are mined on a large scale for the 

 mineral at the village of Graphite in northeastern Warren county. 

 Smaller mines have been operated in other parts of Warren county 

 and in Saratoga county. Small masses of graphite have occasionally 

 been noted in pegmatite. Good six-sided tabular crystals may 

 sometimes be seen in the limestone. 



Hornblende. See amphibole. 



Hypersthene. See pyroxene. 



Ilmenite. Commonly called " Titanic iron ore." It is an oxide 

 of iron and titanium. Seldom in well-defined three or six-sided 

 thick tabular crystals. In many respects much like magnetite (see 

 below), but it is only slightly magnetic and gives the chemical test 

 for titanium. 



Ilmenite occurs in small amounts as scattering grains in most of 

 the Adirondack igneous rocks, but at Lake Sanford, Essex county, 

 there are tremendous deposits of this mineral. 



Limonite. This is a hydrous oxide of iron commonly called " bog 

 iron ore." Many of the Adirondack rocks, when weathered, show 

 brown or yellowish brown colors due to the presence of limonite 

 which has formed during the decomposition of iron-bearing min- 

 erals. Thus the typical, fresh, greenish gray syenite often has a 

 brown outer zone. 



