. Productive soils; the fundamentals of successful soil management and profitable crop production. Soils. 40 HOW EOCKS AND CLIMATE AFFECT SOILS A Rock is an Aggregate of Mineral Particles.—On examining rocks closely we find them composed of mineral particles massed or cemented together.^ In some rocks, as sandstone, the particles are mostly of the same kind. In others they are of different kinds. In a granite, for example, the dissimilar particles may be easily distinguished by differences in hardness, color and crystal form. They are called "rock-forming ; Rock-f onning Min
. Productive soils; the fundamentals of successful soil management and profitable crop production. Soils. 40 HOW EOCKS AND CLIMATE AFFECT SOILS A Rock is an Aggregate of Mineral Particles.—On examining rocks closely we find them composed of mineral particles massed or cemented together.^ In some rocks, as sandstone, the particles are mostly of the same kind. In others they are of different kinds. In a granite, for example, the dissimilar particles may be easily distinguished by differences in hardness, color and crystal form. They are called "rock-forming ; Rock-f onning Minerals of Many Kinds.—We shall not attempt to study all the many kinds of minerals of which rocks are com- posed, but only the more common and important ones as are given in the following table: The Common and Important Rock Minerals Minerals Feldspars Quartz Micas Hornblende, angite, etc. Calcite Dolomite Apatite Hematite Pyrite Gypsum >aU others. Relative abundance in crust of earth, %. Elements of which they are composed (p. 30) Si, Al, Na, Ca, K, 0. Si, 0. Si, Al, Na, Ca, Fe, Mg, K, 0. Si, Al, Na, Ca, Fe, Mg, 0. Ca, 0, C. Ca, Mg, 0, C. Ca, P, 0, Fl. Fe, 0. Fe, S. Ca, S, O. A study of the chemical composition of these rock minerals will make clear to us the source of the mineral elements necessary for plant growth. No nitrogen is found in any of these minerals. Quartz particles are the grains of which sandstones are mostly formed. Why Some Soils Are Deficient in Some of the Important Mineral Elements.—^A sandy soil composed of quartz sand, or derived from pure sandstone would naturally contain only a very small amount of the important mineral elements. Why? Soils composed of mineral particles derived from rocks contain- ing such minerals as feldspars, hornblende, micas, apatite, etc., are usually well supplied with the mineral plant-food elements. The fact that peat soils do not contain any appreciable amount Lava or glassy rocks are Please note that the
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