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Minerals The Building Blocks of Rocks Chapter 3 Minerals The Building Blocks of Rocks

Introduction What is a mineral? A mineral is Naturally Inorganic Crystalline solid Characteristic physical properties Specific chemical composition. Gemstones – precious or semi-precious minerals or rocks used for decorative purposes Fig. 3.1 a, p. 62 3

Introduction Are amber and pearls minerals? Amber is considered a semiprecious “stone,” but it is not a mineral because it is organic and not crystalline. Pearls, although they grow in mollusks, are minerals because they are crystalline and meet the other criteria for minerals. Fig. 3.1 b-c, p. 62 4

Matter – What is It? Atoms and Elements All matter is composed of chemical elements, which are themselves composed of atoms. Atoms consist of a nucleus, of protons and neutrons, and electrons that circle the nucleus. Elements are defined on the basis of the number of protons in the nucleus of an atom (i.e., the atomic number). Another characteristic of an atom is its atomic mass, the sum of the numbers of protons and neutrons in the nucleus. 5

Matter – What is It? What are the atomic number and atomic mass of an atom? The number of protons in an atom’s nucleus determines its atomic number, whereas an atom’s atomic mass number is the total number of protons and neutrons in the nucleus. For example, if an atom has 6 protons and 8 neutrons its atomic number and mass numbers are 6 and 14, respectively. Fig. 3.4, p. 64 6

Nucleus 6 p 6 n 12C (Carbon 12) 13C (Carbon 13) 6 p 7 n 6 p 8 n Figure 3.4: Carbon Isotopes. Schematic representation of the isotopes of carbon. Carbon has an atomic number of 6 and an atomic mass number of 12, 13, or 14, depending on the number of neutrons in its nucleus. Stepped Art Fig. 3-4, p. 64

Matter – What is It? Bonding and Compounds Atoms are joined to one another by forces known as bonding. Atoms of different elements which are bonded to one another form compounds. Fig. 3.5a, p. 65 8

Matter – What is It? Bonding and Compounds Ionic Bonds - Ionic bonds transfer ions, with opposite electrical charges attracting one another Halite is a compound formed by the bonding of sodium atoms to chlorine atoms. Fig. 3.5, p. 65 9

+ – electron transfer Sodium atom 11 p+ 11 e– Chlorine atom 17 p+ ion 11 p+ 10 e– + Chlorine ion 17 p+ 18 e– – Figure 3.5: Ionic Bond to Form the Mineral Halite (NaCl). Stepped Art Fig. 3-5a, p. 65

Matter – What is It? Bonding and Compounds Covalent Bonds - Covalent bonds atoms share electrons. Fig. 3.6, p. 66 11

Matter – What is It? Bonding and Compounds Metallic Bonds Metallic bonds result from extreme electron sharing. Van der Waals bonds Van der Waals bonds are an extremely weak bond without available electrons to form an attraction. 12

Explore the World of Minerals Naturally Occurring Inorganic Substances We define a mineral as naturally occurring This excludes all synthetic substances made by man like synthetic diamonds and rubies. The term inorganic deserves special consideration Animal and plant matter are not minerals Certain organisms, however, do use minerals, like calcite and quartz, to form their shells 13

Explore the World of Minerals Mineral Crystals Why is it that not all mineral specimens show well-developed crystals but all are crystalline solids? As minerals form and grow, they may merge with one another to form a mosaic of interlocking crystalline solids that show no obvious crystals. Nevertheless, individual minerals within this mosaic have their atoms arranged in a specific three-dimensional framework. Fig. 3.8 a-b, p. 67 14

Explore the World of Minerals Chemical Composition of Minerals By definition native elements are made up of only one chemical element, such as gold (Ag) and diamond (C). Most minerals are composed of two or more chemical elements, such as quartz (SiO²). Geo-inSight 6., p. 73 15

Mineral Groups Recognized by Geologists How Many Minerals Are There? Even though there are 92 naturally occurring elements, only 8 of them are very common in Earth’s crust. Even among these 8, oxygen and silicon are by far the most common. Most common minerals are made up of oxygen, silicon, and one or more other elements. Fig. 3.10, p. 69 16

Mineral Groups Recognized by Geologists Most of the more than 3,500 known minerals are silicates (compounds of silicon and oxygen, and other elements). Additional common mineral groups include carbonates, oxides, sulfides, sulfates, and halides. Table 3.1, p. 69 17

Mineral Groups Recognized by Geologists Silicate Minerals composed of the silica tetrahedra Fig. 3.12, p. 70 18

Mineral Groups Recognized by Geologists Silicate Minerals Ferromagnesian silicates - made up of iron, magnesium, or both combined with other elements. dark in color and dense Fig. 3.12 a, p. 70 Fig. 3.13 a, p. 74 19

Mineral Groups Recognized by Geologists Silicate Minerals Nonferromagnesian silicates - lack iron and magnesium light colored Fig. 3.11, p. 70 Fig. 3.13 b, p. 74 20

Mineral Groups Recognized by Geologists Carbonate Minerals All carbonate minerals have the carbonate radical (CO³)-² as in calcite (CaCO³) and dolomite [CaMg(CO³)²]. Carbonate minerals are found mostly in the sedimentary rocks limestone and dolostone. Carbonates are derived from the shells and hard parts of marine organisms or are precipitated from seawater as evaporites. Fig. 3.11, p. 70 Fig. 3.14, p. 75 21

Mineral Groups Recognized by Geologists Other Mineral Groups Native Elements All native elements are composed of a single element. Gold, copper and diamonds commonly occur as native elements. Geo-inSight 6., p. 73 22

Mineral Groups Recognized by Geologists Other Mineral Groups Sulfides All sulfide minerals contain sulfur plus a metallic element as in galena (PbS) and pyrite (FeS²). Sulfide minerals are found in all types of rocks. They commonly form along mid-oceanic ridges Fig. 3.14b, p. 75 Fig. 3.15a, p. 78 23

Mineral Groups Recognized by Geologists Other Mineral Groups Sulfates All sulfate minerals have the sulfate radical (SO4 -² ) as in gypsum (CaSO4 2H2O) Sulfate minerals are common in deserts, forming from evaporation of water Fig. 3.11, p. 70 24

Physical Properties of Minerals Mineral composition and structure produce unique physical properties. Color Hardness Cleavage Crystal form Specific gravity p. 60 25

Physical Properties of Minerals Luster and Color Luster is the quality and intensity of light reflected from a mineral and is characterized as metallic or nonmetallic. Color, in contrast, is a visual quality of minerals that results from the way they absorb or transmit light. Fig. 3.15a, c, p. 78 26

Physical Properties of Minerals Crystal Form Crystal form is useful for the identification of minerals that typically show well-developed crystals. For many other minerals, however, the crystals grow in proximity to form a crystalline mass, in which case other mineral properties such as luster, hardness, and cleavage must be used for identification. Fig. 3.7, p. 67 27

Physical Properties of Minerals Cleavage and Fracture Mineral cleavage refers to the breakage or splitting of mineral crystals along one or more smooth planes determined by atomic structure. When used with other mineral properties, cleavage can distinguish between minerals that otherwise look much the same. Fracture refers to the irregular breakage of a mineral Fig. 3.16, p. 79 28

Cleavage in one direction Micas—biotite and muscovite Cleavage in Cleavage plane Micas—biotite and muscovite Cleavage in two directions at right angles Potassium feldspars, plagioclase feldspars Cleavage in three directions at right angles Halite, galena Cleavage in three directions, not at right angles Calcite, dolomite Cleavage in four directions Fluorite, diamond Cleavage in six directions Sphalerite Stepped Art Fig. 3-16, p. 79

Physical Properties of Minerals Hardness Mohs hardness scale Ten minerals are used to compare the hardness between all the rest. Table 3.2, p. 79 30

Physical Properties of Minerals Specific Gravity (Density) - The specific gravity is a way to describe how heavy a mineral is. Specific gravity is the ratio of the weight of a mineral to an equal volume of water. For example, galena has a specific gravity of 7.58 gm/cm3. It is 7.38 times as heavy as an equal volume of water. Fig. 3.14b-c, p. 75 31

Physical Properties of Minerals Other Useful Mineral Properties Feel - talc Taste - halite Magnetism - magnetite Double refraction - calcite React to dilute hydrochloric acid – calcite, dolomite 32

Rock-Forming Minerals How do rock-forming minerals differ from accessory minerals? A few minerals are common enough to be known as rock-forming minerals. Most of these are silicates. Accessory minerals can be ignored in this endeavor because they are present in minor quantities. Table 3.3, p. 80 33

Rock-Forming Minerals Common rock forming minerals Fig. 3.19, p.80 34

How Do Minerals Form? As molten rock material known as magma (lava at the surface) cools, minerals begin to crystallize and grow This determines the composition of various igneous rocks. Fig. 3.19, p. 80 35

Natural Resources and Reserves How does a resource differ from a reserve? A resource is any solid, liquid, or gaseous substance in rocks whose profitable extraction is potentially feasible. Many resources are concentrations of economically important minerals. A reserve is only that part of the resource base that can be extracted economically. 36

Natural Resources and Reserves While the United States is dependent on imports for many mineral resources, Canada is more self-reliant. Fig. 3.20, p. 81 37

Natural Resources and Reserves What factors affect the status or a resource? Market price is the most obvious determinate of whether a commodity is classified as a resource or reserve Other factors include geographic location, labor costs, and developments in science and technology. 38

End of Chapter 3