APPENDIX 



SOME COMMON ADIRONDACK MINERALS 



A mineral is a homogeneous, natural substance with a definite 

 chemical composition, and usually in solid form. Nearly a thousand 

 well-defined species are known. 



A crystal is a mineral with a regular external form bounded by 

 plane faces and possessing a definite internal structure. Crystals 

 commonly develop from ordinary solutions or during the cooling of 

 molten masses of rock. 



Mineral cleavage is the tendency of certain minerals to break 

 along more or less smooth, plane surfaces in one or more direc- 

 tions. 



Amphibole. Crystals usually in short stout prisms, the prismatic 

 faces meeting at 124 degrees. Two good cleavages at 124 degrees. 

 Color commonly brown to black, but sometimes white or green. 

 Some varieties can just be scratched by a knife, others can not. 

 Hornblende, the most common variety, is a silicate of lime, magneisa, 

 iron, aluminum etc., and is dark colored. Tremolite is a silicate 

 of lime and magnesia, and is white. 



Hornblende is very abundant in the Adirondack region, being a 

 prominent constituent of the syenite-granite series ; some dark 

 phases of the anorthosite ; gabbro ; and many of the Grenville 

 gneisses. Well-formed crystals are not common. Tremolite is 

 much rarer, but occurs locally in certain Grenville strata, especially 

 those associated with limestone. 



Apatite. Crystals are hexagonal prisms capped by six-sided 

 pyramids. Just hard enough to scratch glass. No good cleavage. 

 Color, greenish, bluish green or brown. Composition, a phosphate 

 of lime. 



\\'ell-formed microscopic crystals are common in the Adirondack 

 igneous rocks and in certain of the Grenville gneisses. Locally, 

 crystals from a fraction of an inch to several inches long are 

 developed in the Grenville limestone. 



Asbestos. See sepentine. 



Augite. See pyroxene. 



Biotite. See mica. 



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