Rocks

Wearing Down and Building Up the Earth’s Surface Weathering is an external process that wears the earth’s surface down. Figure 15-6

MINERALS, ROCKS, AND THE ROCK CYCLE The earth’s crust consists of solid inorganic elements and compounds called minerals that can sometimes be used as resources. Mineral resource: is a concentration of naturally occurring material in or on the earth’s crust that can be extracted and processed into useful materials at an affordable cost.

General Classification of Nonrenewable Mineral Resources The USGS classifies them into four major categories: Identified: known location, quantity, and quality or existence known based on direct evidence and measurements. Undiscovered: potential supplies that are assumed to exist. Reserves: identified resources that can be extracted profitably. Other: undiscovered or identified resources not classified as reserves

Decreasing cost of extraction Undiscovered Identified Economical Reserves Other resources Decreasing cost of extraction Not economical Figure 15.7 Natural capital: general classification of nonrenewable mineral resources. (The area shown for each class does not represent its relative abundance.) Hypothetically, other resources could become reserves because of rising mineral prices or improved mineral location and extraction technology. In practice, geologists expect only a fraction of these resources to become reserves. QUESTION: How might this classification scheme change if a full-blown nanotechnology revolution (p. 335) takes place over the next two decades? Decreasing certainty Known Existence Fig. 15-7, p. 341

GEOLOGIC PROCESSES Deposits of nonrenewable mineral resources in the earth’s crust vary in their abundance and distribution. A very slow chemical cycle recycles three types of rock found in the earth’s crust: Sedimentary rock (sandstone, limestone). Metamorphic rock (slate, marble, quartzite). Igneous rock (granite, pumice, basalt). In the ROCK CYCLE

Igneous rock Granite, pumice, basalt Erosion Transportation Weathering Deposition Igneous rock Granite, pumice, basalt Sedimentary rock Sandstone, limestone Heat, pressure Cooling Heat, pressure, stress Magma (molten rock) Figure 15.8 Natural capital: the rock cycle is the slowest of the earth’s cyclic processes. The earth’s materials are recycled over millions of years by three processes: melting, erosion, and metamorphism, which produce igneous, sedimentary, and metamorphic rocks. Rock from any of these classes can be converted to rock of either of the other two classes, or can be recycled within its own class. QUESTION: List three ways that the rock cycle benefits your lifestyle. Melting Metamorphic rock Slate, marble, gneiss, quartzite Fig. 15-8, p. 343

ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES Figure 15-9

Natural Capital Degradation Extracting, Processing, and Using Nonrenewable Mineral and Energy Resources Steps Environmental effects Mining Disturbed land; mining accidents; health hazards, mine waste dumping, oil spills and blowouts; noise; ugliness; heat Exploration, extraction Processing Transportation, purification, manufacturing Solid wastes; radioactive material; air, water, and soil pollution; noise; safety and health hazards; ugliness; heat Use Figure 15.10 Natural capital degradation: some harmful environmental effects of extracting, processing, and using nonrenewable mineral and energy resources. The energy required to carry out each step causes additional pollution and environmental degradation. Transportation or transmission to individual user, eventual use, and discarding Noise; ugliness; thermal water pollution; pollution of air, water, and soil; solid and radioactive wastes; safety and health hazards; heat Fig. 15-10, p. 344

ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES A variety of mining methods are used based on mineral depth. Surface mining: shallow deposits are removed. Subsurface mining: deep deposits are removed.

Open-pit Mining Machines dig holes and remove ores, sand, gravel, and stone. Toxic groundwater can accumulate at the bottom. Figure 15-11

Area Strip Mining Earth movers strips away overburden, and giant shovels removes mineral deposit. Often leaves highly erodible hills of rubble called spoil banks. Figure 15-12

Contour Strip Mining Used on hilly or mountainous terrain. Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall. Figure 15-13

Undisturbed land Overburden Highwall Coal seam Overburden Pit Bench Figure 15.13 Natural capital degradation: contour strip mining of coal used in hilly or mountainous terrain. Spoil banks Fig. 15-13, p. 346

Mountaintop Removal Machinery removes the tops of mountains to expose coal. The resulting waste rock and dirt are dumped into the streams and valleys below. Figure 15-14

Mining Impacts The ores are not pure Metal ores are smelted or treated with (potentially toxic) chemicals to extract the desired metal. Figure 15-15

SUPPLIES OF MINERAL RESOURCES The future supply of a resource depends on its affordable supply and how rapidly that supply is used. A rising price for a scarce mineral resource can increase supplies and encourage more efficient use.

Depletion time A Depletion time B Depletion time C Mine, use, throw away; no new discoveries; rising prices Recycle; increase reserves by improved mining technology, higher prices, and new discoveries B Production Recycle, reuse, reduce consumption; increase reserves by improved mining technology, higher prices, and new discoveries C Figure 15.16 Natural capital depletion: depletion curves for a nonrenewable resource (such as aluminum or copper) using three sets of assumptions. Dashed vertical lines represent times when 80% depletion occurs. Present Depletion time A Depletion time B Depletion time C Time Fig. 15-16, p. 348

SUPPLIES OF MINERAL RESOURCES New technologies can increase the mining of low-grade ores at affordable prices, but harmful environmental effects can limit this approach. Most minerals in seawater and on the deep ocean floor cost too much to extract, and there are squabbles over who owns them.

Getting More Minerals from the Ocean Hydrothermal deposits form when mineral-rich superheated water shoots out of vents in solidified magma on the ocean floor. Figure 15-17

USING MINERAL RESOURCES MORE SUSTAINABLY Scientists and engineers are developing new types of materials as substitutes for many metals. Recycling valuable and scarce metals saves money and has a lower environmental impact then mining and extracting them from their ores.