COMPOSITION OF SIMPLE MINERALS. 
39 
The same remarks might be made in regard to the Southern highlands. Granitic soil 
must be confined to the fields 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 are 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: 
Labradorite. 
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. 
