About Earth Materials

Transcription

1 Grotzinger Jordan Understanding Earth Sixth Edition Chapter 3: EARTH MATERIALS Minerals and Rocks 2011 by W. H. Freeman and Company About Earth Materials All Earth materials are composed of atoms bound together. Minerals are composed of atoms bonded together and are the building blocks of rocks. Rocks are composed of minerals and they record various geologic processes. 1

2 1. What Are Minerals? Minerals are the building blocks of rocks. Geologists define mineral as a naturally occurring, solid, crystalline substance, usually inorganic, with a specific chemical composition. 1. What Are Minerals? Naturally occurring = found in nature )but also produced by industrial and pre-industrial processes) Solid, crystalline substance = atoms are arranged in orderly patterns (but there are exceptions) Usually inorganic = not a product of living tissue (but can be biological) With a specific chemical formula = unique chemical composition 2

3 2. The Structure of Matter The atom is the smallest unit of an element that retains the physical and chemical properties of that element. Atomic nucleus: : protons and neutrons. Electrons: : cloud of moving particles surrounding the nucleus. Example: the carbon atom (C) The Carbon Atom electron cloud atomic nucleus Carbon has 6 electrons and a nucleus of 6 protons and 6 neutrons having no charge. electron ( ) proton (+) neutron 3

4 2. The Structure of Matter Isotopes atoms of the same element with different numbers of neutrons. Example: the carbon atom (C) typically has 6 neutrons and 6 protons (called C 12 ), but there are also small amounts of C 13 and C The Structure of Matter Chemical reactions interactions of the atoms of two or more elements in certain fixed proportions. Example: H + H + O = H 2 O Example: Na + Cl = NaCl 4

5 2. The Structure of Matter Chemical compounds that are minerals form by: electron sharing or electron transfer Electron Sharing: Carbon atoms in a diamond 5

6 Electron Transfer: Sodium (Na) + chlorine (Cl( Cl) ) = NaCl (halite) Electron Transfer: Sodium (Na) + chlorine (Cl( Cl) ) = NaCl (halite) Each sodium ion (circled in red) is surrounded by 6 chloride ions (circled in yellow), and vice versa. Compounds of different atoms built through electron transfer or sharing or compounds of the same atom are molecules 6

7 3. The Structure of Minerals How do minerals form? Crystallization atoms come together in the proper proportion and proper arrangement Electrical charges of atomic ions Cation positively charged Anion negatively charged Atomic ions arrange themselves according to charge and size. 3. The Structure of Minerals The forces of electrical attraction between protons (+) and electrons (-)( that hold minerals and other chemical compounds together Google the bonding: The web is filled with covalent bonds great examples, ionic bonds including YouTube metallic bonds movies! 7

8 3. The Structure of Minerals covalent bond A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms The Structure of Minerals ionic bond An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions.. Ionic bonds are formed between a cation,, which is usually a metal, and an anion, which is usually a nonmetal. Na + Cl Na + + Cl NaCl 8

9 3. The Structure of Minerals metallic bond Metallic bonding constitutes the electrostatic attractive forces between the delocalized, free electrons,, called conduction electrons,, or "electron sea", and the positively charged metal ions. Sharing of "free" electrons among a lattice of positively charged ions (cations( cations) The Structure of Minerals 9

10 3. The Structure of Minerals When do minerals form? During cooling of molten rock During evaporation of water Upon changes in temperature and pressure on existing minerals 4. Classes of Rock-forming Minerals Chemical classes of minerals: 1. Silicates contain O and Si 2. Carbonates contain C and O 3. Oxides contain O and metallic cations 4. Sulfides contain S and metallic cations 5. Sulfates contain SO 4 and metallic cations 6. Halides contain Cl,, F, I, or Br 7. Hydroxides contain OH 8. Native elements masses of all the same element metallically bonded 10

11 4. Classes of Rock-forming Minerals Formation of silicate minerals Silicate ion (SiO 4 4 ) The silicate ion forms tetrahedra. Oxygen ions (O 2 ) Silicon ion (Si 4+ ) Silicate ion (SiO 4 4 ) The silicate ion forms tetrahedra. Quartz structure Oxygen ions (O 2 ) Silicon ion (Si 4+ ) Tetrahedra are the basic building blocks of all silicate minerals. About 95% of Earth s minerals are silicates. 11

12 4. Classes of Rock-forming Minerals Types of silicate minerals: Isolated silica tetrahedra Single-chain linkages Double-chain linkages Sheet linkages Frameworks Mineral Chemical formula Cleavage planes and number of cleavage directions Silicate structure Specimen Olivine (Mg, Fe) 2 SiO 4 1 plane Isolated tetrahedra 2 planes at 90 Single chains Pyroxene (Mg, Fe)SiO 3 2 planes at 60 and 120 Double chains Amphibole Ca 2 (Mg, Fe) 5 Si 8 O 22 (OH) 2 Micas Feldspars Muscovite: KAl 2 (AlSi 3 O 10 )(OH) 2 Biotite: K(Mg, Fe) 3 AlSi 3 O 10 (OH) 2 Orthoclase feldspar: KAlSi 3 O 8 Plagioclase feldspar: (Ca, Na) AlSi 3 O 8 1 plane Sheets 2 planes at 90 Three-dimensional framework 12

13 5. Physical Properties of Minerals Hardness Cleavage Fracture Luster Color Streak Density Crystal habit 13

14 5. Physical Properties of Minerals Uses of physical properties: Mineral identification Industrial application of minerals 14

15 5. Physical Properties of Minerals Mica and its cleavage 5. Physical Properties of Minerals Pyrite and its crystal habit 15

16 5. Physical Properties of Minerals Calcite and its cleavage 5. Physical Properties of Minerals 16

17 5. Physical Properties of Minerals Hematite and its streak 6. What Are Rocks? Rocks are naturally occurring solid aggregates of minerals, or in some cases, non-mineral solid matter. Identity is determined by: texture composition 17

18 6. What Are Rocks? Rocks are classified into three groups: Igneous Sedimentary Metamorphic 6. What Are Rocks? 18

19 Igneous Rocks (magmatic rocks) 19

20 Sedimentary Rocks 20

21 Metamorphic Rocks 7. The Rock Cycle & Plate Tectonics Interactions between the plate tectonic and climate systems 21

22 7. The Rock Cycle & Plate Tectonics 7. The Rock Cycle & Plate Tectonics 22

23 7. The Rock Cycle & Plate Tectonics 7. The Rock Cycle & Plate Tectonics 23

24 7. The Rock Cycle & Plate Tectonics 7. The Rock Cycle & Plate Tectonics 24

25 8. Concentrations of Valuable Mineral Resources Types of ore minerals: Vein deposits Disseminated deposits Igneous deposits Sedimentary deposits Groundwater dissolves metal oxides and sulfides. Heated by the magma, it rises, precipitating metal ores in joints. Deformed country rock Geysers and hot springs Magma Groundwater Plutonic intrusion 25

26 Groundwater dissolves metal oxides and sulfides. Heated by the magma, it rises, precipitating metal ores in joints. Deformed country rock Geysers and hot springs Vein deposit Magma Groundwater Plutonic intrusion 8. Concentrations of Valuable Mineral Resources Typical sulfide minerals from vein deposits 26

27 8. Concentrations of Valuable Mineral Resources Open-pit pit mine for disseminated deposits of copper-bearing minerals. 8. Concentrations of Valuable Mineral Resources Igneous deposits Chromite layers (dark) in layered igneous rock 27

28 8. Concentrations of Valuable Mineral Resources Sedimentary deposits: Copper, iron, other metals Gold, diamonds, other heavy minerals (placers) Thought questions for this chapter Coal, a natural organic substance that forms from decaying vegetation, is not considered to be a mineral. However, when coal is heated to high temperatures and buried under high pressures, it is transformed into the mineral graphite. Why is it, then, that coal is not considered a mineral, but graphite is? Explain your reasoning. What is the difference between graphite and diamond? Draw a simple diagram to show how silicon and oxygen in silicate minerals share electrons. 28

29 Thought questions for this chapter Aragonite, with a density of 2.9 g/cm 3, has exactly the same chemical composition as calcite, which has a density of 2.7 g/cm 3. Which of these two minerals is more likely to have formed under high pressure? There are at least seven physical properties one can use to identify an unknown mineral. Which ones are most useful in discriminating between minerals that look similar? Describe a strategy that would allow you to prove that an unknown clear calcite crystal is not the same mineral as a known clear crystal of quartz. Choose two minerals that you think might make good abrasive or grinding stones for sharpening steel and explain why? Thought questions for this chapter In some bodies of granite, we can find very large crystals, some as much as a meter across, yet these crystals tend to have few crystal faces. What can you deduce about the conditions under which these large crystals grew? Which igneous intrusion would you expect to have a wider contact metamorphic zone: one intruded by a very hot magma or one intruded by a cooler magma? Where are igneous rocks most likely to be found? How could you be certain that the rocks were igneous and not sedimentary or metamorphic? 29

30 Thought questions for this chapter Diopside,, a pyroxene, has the formula (Ca, Mg) 2 Si 2 O 6. What does that tell you about its crystal structure and cation substitution? What physical properties of sheet silicates are related to their crystal structure? Thought questions for this chapter What geologic processes transform a sedimentary rock into an igneous rock? Describe the geologic processes by which an igneous rock is transformed into a metamorphic rock and then exposed to erosion. Using the rock cycle, trace the path from a magma to a granitic intrusion to a metamorphic gneiss to a sandstone. Be sure to include the roles of the plate tectonics climate systems and the specific processes that create rocks. 30

31 Thought questions for this chapter Back in the late 1800s, gold miners used to pan for gold by placing sediment from rivers in a pan and filtering water through the pan while swirling the pan s s contents. The miners wanted to be certain that they had found real gold and not pyrite ( fool( fool s s gold ). Why did this method work? What mineral property does the process of panning for gold use? What is another possible method for distinguishing between gold and pyrite? Repeat the key terms and concepts Anion Atomic mass Atomic number Bedding Biological sediment Carbonate Cation Chemical sediments Cleavage Color Contact metamorphism Covalent bond Crystal Crystal habit 31

32 Repeat the key terms and concepts Density Disseminated deposit Electron sharing Electron transfer Erosion Fracture Grain Hardness Hydrothermal solution Igneous rock Ion Ionic bond Isotope Lithification Repeat the key terms and concepts Luster Magma Metallic bond Metamorphic rock Mineral Mineralogy Mohs scale of hardness Ore Oxides Polymorph Precipitate Regional metamorphism Rock Rock cycle 32

33 Repeat the key terms and concepts Sediment Sedimentary rock Silicate Siliclastic sediments Specific gravity Streak Sulfate Sulfide Texture Trace element Vein Weathering 33