110 HOW CROPS FEED. 
The following analyses represent these varieties. 
MuscovirTeE. PHLOGOPITE. BIorire. 
Litchfield, Mt.Leinster, Edwards, N. Burgess, Putnam Co., ae 
Conn. Ireland. N. Y. Canada, N.Y. Siberia, 
Smith & Brush. Hanghton. W.J.Craw. T.S.Hunt, Smith & Brush. H. Rosé. 
Silica, 44.60 44.64 40.36 40.97 389.62 40.00 
Alumina, 36.23 30.18 16.45 18.56 17.35 12.67 
Oxide ofiron, 1.34 6.35 trace — 5.40 19.08 
Oxide of ere pee cn 0.68 
manganese, 
Magnesia, 0.387 0.72 29.55 25.80 23.85 15.70 
Lime, 0.50 — — — — —_ 
Potash, 6.20 12.40 1.23 8.26 8.95 5.61 
Soda, 4.10 — 4.94 1.08 1.01 — 
Water, 5.26 5.32 0.95 1.00 1.41 — 
Variable Composition of Minerals.—We notice in the 
micas that two analyses of the same species differ very 
considerably in the proportion, and to some extent in the 
kind, of their ingredients. Of the two mugcovites the 
first contains 6°|, more of alumina than the second, while 
the second contains 5°|, more of oxide of iron than the 
first. Again, the second contains 12.4°|, of potash, but no 
soda and no lime, while the first reveals on analysis 4°|, of 
soda and 0.5°|, of lime, and contains correspondingly less 
potash. Similar differences are remarked in the other anal- 
yses, especially in those of Biotite. 
In fact, of the analyses of more than 50 micas which are 
given in mineralogical treatises, scarcely any two per- 
fectly agree. The same is true of many other minerals, 
especially of the amphiboles and pyroxenes presently to be 
noticed. In accordance with this variation in composition 
we notice extraordinary diversities in the color and ap- 
pearance of different specimens of the same mineral. 
This fact may appear to stand in contradiction to the 
statement above made that these minerals are definite 
combinations. In the infancy of mineralogy great per- 
plexity arose from the numerous varieties of minerals that 
were found—varieties that agreed together in certain char- 
acteristics, but widely differed in others. 
