COMPOSITION OF SIMPLE MINERALS. 39 



The same remarks might be made in regard to the Southern highlands. Granitic soil 

 must be confined to the (it-Ids underlaid by primary rocks ; those which contain felspar 

 and mica, and which furnish by decomposition one or more of the alkalies or alkaline 

 earths. Besides felspar, there arc other minerals which are agriculturally important; thus, 

 albite (another variety of the felspar family) , mica and hornblende, are each important 

 minerals to be known, or to be sought for in the rock, if we would learn approximately 

 the composition of the soil of a primary district. Thus in Gouverneur and the neighboring 

 towns in St. Lawrence county, a granite occurs, containing considerable albite. This 

 substance contains soda in the place of potash ; and hence we might expect this element 

 in granitic soils, especially as this kind of granite is rather disposed to disintegrate. 



§ 3. Composition of simple minerals. 



The composition of felspar and albite, together with that of some of the other more 

 common rocks, it may be well to state in this place. The two first named consist respec- 

 tively of 



Felspar. Albite. 



Silica, 65.21 69.09 



Alumina, 18.13 19.22 



Potash, 16.66 



Soda, . 11.69 



100.00 100.00 



In attempting to distinguish these minerals from quartz, or flint as it is often called, we 

 are to notice their hardness. Felspar and albite just scratch common window glass, but 

 quartz does not. Albite is always white; felspar is white or flesh-colored, and each give 

 a strong reflection of light from the planes of the crystal ; while quartz has the lustre of 

 glass, or more of a vitrified appearance in the mass. 



Another kind of felspar is the labradorite, which abounds in the rocks of the Adirondack 

 mountains. The rock itself, as already stated, is termed hypersthene rock, from a small 

 quantity of this mineral which it contains. The whole mass is mostly labradorite ; and 

 by decomposing, it has formed in some places an imperfect porcelain clay. Its composi- 

 tion is as follows : 



Labhadorite. 



Silica. 55.75 



Alumina, 26.50 



Lime, _ __ 11.00 



Iron, 1.25 



Soda, 4.00 



98.50 Klaproth. 



This species is usually smoke-grey, though the exposed surface of the rock is grey or 

 greyish white : it appears to be bleached. 



