Chapter 3 Summary and Key Terms (PDF)

Chapter 3 Summary Matter is composed of chemical elements, each of which consists of atoms. Protons and neutrons are present in an atom’s nucleus, and electrons orbit around the nucleus in electron shells. The number of protons in an atom’s nucleus determines atomic number. The ato...

Chapter 3 Summary Matter is composed of chemical elements, each of which consists of atoms. Protons and neutrons are present in an atom’s nucleus, and electrons orbit around the nucleus in electron shells. The number of protons in an atom’s nucleus determines atomic number. The atomic mass number is the number of protons plus neutrons in the nucleus. Atoms of the same chemical element may have different atomic mass numbers because the number of neutrons can vary. The atoms of an element that have different atomic mass numbers are called isotopes. Bonding results when atoms join with other atoms; different elements bond to form compounds. With few exceptions, minerals are compounds. Ionic and covalent bonds are the most common types of bonds in minerals, but metallic and van der Waals bonds are also found in some minerals. Minerals are naturally occurring, inorganic crystalline solids with narrowly defined chemical compositions and characteristic physical properties. The criterion naturally occurring excludes from minerals all substances manufactured by humans, such as synthetic diamonds and rubies. The constituent atoms of minerals are arranged in a regular, three-dimensional framework. Mineral composition is indicated by a chemical formula, such as SiO2 for quartz. Some minerals have a range of compositions because different elements substitute for one another if their atoms are about the same size and have the same electrical charge. Structure and composition control the physical properties of minerals, such as luster, crystal form, hardness, color, cleavage, fracture, and specific gravity. More than 5000 minerals are known, and most of them are silicates. The basic building block of all silicate minerals is the silica tetrahedron, consisting of one  silicon atom and four oxygen atoms. Because a silica tetrahedron has a negative charge, it does not exist in nature as an isolated ion group; rather, it combines with positively charged ions or shares its oxygen atoms with other silica tetrahedra. The two types of silicates are ferromagnesian (iron or magnesium-containing) and nonferromagnesian. Carbonate minerals are those that contain the negatively charged carbonate radical and include calcium carbonate as the minerals aragonite or calcite. In addition to silicates and carbonates, geologists recognize native elements, hydroxides, oxides, phosphates, halides, sulfates, and sulfides. Geologists define luster as metallic (having the appearance of a metal) and nonmetallic. Many mineral specimens do not show the perfect crystal form typical of their mineral species. Nevertheless, some minerals typically occur as crystals. Cleavage is characterized in terms of quality (perfect, good, poor), direction, and the angles of intersection of cleavage planes. In contrast to cleavage, fracture is mineral breakage along irregular surfaces. Relative hardness is easily determined by the use of the Mohs hardness scale. A mineral’s specific gravity is the ratio of its weight to the weight of an equal volume of pure water at 4°C. Density, in contrast, is a mineral’s mass (weight) per unit of volume  expressed in grams per cubic centimeter. A rock is a solid aggregate of one or more minerals, but the term also refers to masses of mineral-like matter and solid organic matter. A few minerals, designated rock-forming minerals, are common enough in rocks to be essential to their identification and classification. Most rock-forming minerals are silicates, but some carbonates are also common. Several processes account for the origin of minerals, including the cooling of magma, weathering, the evaporation of seawater, metamorphism, and organisms using substances dissolved in seawater to build their shells. Many resources are concentrations of minerals or rocks of economic importance. They are further characterized as metallic resources, nonmetallic resources, and energy resources. Reserves are that part of the resource base that is known and can be extracted profitably. Distinguishing a resource from a reserve depends on market price, labor costs, geographic location, and developments in science and technology. The United States must import many resources to maintain its industrial capacity. Key Terms Atom Electron Nonferromagnesian silicate Atomic mass number Electron shell Nucleus Atomic number Element Proton Bonding Ferromagnesian silicate Reserve Carbonate mineral Hardness Resource Cleavage Ion Rock Compound Ionic bond Rock-forming mineral Covalent bond Luster Silica Crystal Matter Silica tetrahedron Crystalline solid Mineral Silicate Density Neutron Specific gravity