to Answers Review Questions
1. In short, the magma from which igneous rocks form may be produced when any rock is melted. Sedimentary rocks are formed from the weathered products of preexisting rocks, whether igneous, metamorphic, or sedimentary. Finally, metamorphic rocks are created when any rock type undergoes metamorphism. 2. Basalt would be the probable rock type for the lava flow, since extrusive rock cools rapidly, yielding a fine-grained texture. If the same magma cooled below the surface, gabbro, the coarse-grained equivalent of basalt, would form. 3. It indicates that the magma likely changed environments and cooled at two different rates, yielding crystals of two distinctively different sizes. 4. Although both have the same mineral composition, granite is coarse-grained (intrusive), whereas rhyolite is fine-grained (extrusive). 5. Minerals that crystallize at about the same time (temperature) are most often found together in the same igneous rock. 6. Quartz and clay minerals are the chief constituents of detrital sedimentary rocks. Clay minerals are the most abundant product of chemical weathering. Quartz is an abundant sediment because it is very resistant to chemical weathering. When granite and other quartz-rich rocks are chemically weathered, quartz grains are set free. 7. Particle size is the primary basis for distinguishing among the various detrital sedimentary rocks. 8. Material dissolved in water is the source of chemical sediment. This material may be precipitated either directly as the result of inorganic processes such as evaporation or indirectly as the result of life processes of water-dwelling organisms. In the latter case, the sediment is said to be biochemical in origin. 9. Evaporites are chemical sedimentary rocks in which the mechanism triggering deposition is evaporation. Examples include rock salt and rock gypsum.
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Rocks: Materials of the Solid Earth
10. Compaction is most significant as a lithification process in fine-grained sedimentary rocks such as shale. 11. Layers, commonly termed strata or beds, are probably the most characteristic feature of sedimentary rocks. 12. Metamorphism is a change in mineral composition and/or texture in a rock in response to changing conditions. 13. The three agents of metamorphism are heat, pressure, and chemically active fluids. Heat is the most important agent of metamorphism because it provides the energy that drives the chemical reactions responsible for mineral and textural changes during metamorphism. causes Pressure spaces between mineral grains to close and existing minerals to recrystallize into new minerals, and often produces a parallel alignment of minerals to produce a layered or banded appearance. Chemically active fluids in metamorphism serve to facilitate the movement of ions during metamorphic reactions. 14. When great quantities of rock are subjected to intense heat and pressure, as occurs during mountain building, regional metamorphism is said to occur. When rock is altered because of its close proximity to a mass of magma (which bakes the rock and may alter the chemical environment), it is said to undergo contact metamorphism. 15. The foliated textures of schist and gneiss would distinguish them from the non-foliated rocks quartzite and marble. 16. They may have a different mineral composition; they may become foliated; the minerals may be larger than before; and they will probably be denser. 17. Hydrothermal solutions can deposit metals as (1) vein deposits in fractures or (2) as disseminated deposits distributed as minute masses throughout an entire rock body. 18. The two broad categories of nonmetallic resources are (1) building materials, which include aggregate, gypsum, and clay, and (2) industrial minerals such as fluorite (used in making steel), common salt, sulfur, corundum (an abrasive), and sylvite (used in the production of fertilizers). Some substances, such as limestone, are found in both groups.
Answers to Earth System Questions
1. The sedimentary rock coquina is a biochemical limestone that consists of loosely cemented shells and shell fragments that have accumulated on the ocean floor. The primary Earth...