core
	The dense, intensely hot mass of molten metal, mostly iron and nickel, thousands of kilometers in diameter at the earth's center.
crust
	The cool, lightweight, outermost layer of the earth's surface that floats on the soft, pliable underlying layers; similar to the "skin" on a bowl of warm pudding.
flood
	An overflow of water onto land that normally is dry.
heap-leach extraction
	A technique for separating gold from extremely low-grade ores. Crushed ore is piled in huge heaps and sprayed with a dilute alkaline-cyanide solution, which percolates through the pile to extract the gold, which is separated from the effluent in a processing plant. This process has a high potential for water pollution.
igneous rocks
	Crystalline minerals solidified from molten magma from deep in the earth's interior; basalt, rhyolite, andesite, lava, and granite are examples.
landslide
	The sudden fall of rock and earth from a hill or cliff. Often triggered by an earthquake or heavy rain.
magma
	Molten rock from deep in the earth's interior; called lava when it spews from volcanic vents.
mantle
	A hot, pliable layer of rock that surrounds the earth's core and underlies the cool, outer crust.
metamorphic rock
	Igneous and sedimentary rocks modified by heat, pressure, and chemical reactions.
mineral
	A naturally occurring, inorganic, crystalline solid with definite chemical composition and characteristic physical properties.
rock cycle
	The process whereby rocks are broken down by chemical and physical forces; sediments are moved by wind, water, and gravity, sedimented and reformed into rock, and then crushed, folded, melted, and recrystallized into new forms.
sedimentary rock
	Deposited material that remains in place long enough or is covered with enough material to compact into stone; examples include shale, sandstone, breccia, and conglomerates.
sedimentation
	The deposition of organic materials or minerals by chemical, physical, or biological processes. Sediments can be transported from their source to their place of deposition by gravity, wind, water, or ice. If subjected to sufficient heat, pressure, or chemical reactions, sediments can solidify into sedimentary rock.
strategic minerals
	Materials a country cannot produce itself but that it uses for essential materials or processes.
tectonic plates
	Huge blocks of the earth's crust that slide around slowly, pulling apart to open new ocean basins or crashing ponderously into each other to create new, larger landmasses.
tsunami
	Giant seismic sea swells that move rapidly from the center of an earthquake; they can be 10 to 20 meters high when they reach shorelines hundreds or even thousands of kilometers from their source.
weathering
	Changes in rocks brought about by exposure to air, water, changing temperatures, and reactive chemical agents.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.