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Rocks and Minerals A First Look

Rocks and Minerals A First Look. Chapter 2. The differences in the physical properties of rocks, minerals, and soils determine their suitability for different purposes – extraction of water or of metals, construction, manufacturing, waste disposal, agriculture, and other uses. Atoms.

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Rocks and Minerals A First Look

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  1. Rocks and MineralsA First Look Chapter 2 The differences in the physical properties of rocks, minerals, and soils determine their suitability for different purposes – extraction of water or of metals, construction, manufacturing, waste disposal, agriculture, and other uses

  2. Atoms • Smallest particle into which an element can be divided while still retaining the chemical characteristics of that element • Composed of a nucleus surrounded by electrons • Nucleus is composed of protons (+) and neutrons (0) • Number of protons defines the chemical element and atomic number ( H = 1, He = 2, Li = 3, …) • Number of neutron adds mass to the atom • Number of electrons (-) orbiting nucleus determined by the number of positively charged protons; • Negatively charged electrons balance the positive charges of the protons

  3. Figure 2.1 Schematic drawing of atomic structure

  4. Elements and Isotopes • Element – substance composed of atoms with the same number of protons • All nuclei, except the simplest hydrogen atoms, contain neutrons • The number of neutrons is similar to or somewhat greater than the number of protons • Isotopes – number of neutrons for and element may not be the same; variable numbers of neutrons possible • Atomic Mass Number is the number of protons and neutrons in the elements nucleus • Some isotopes have more neutron and are heavier (carbon-14 has 6 protons and 8 neutrons) • Some isotopes have fewer neutrons and are lighter (carbon-12 has 6 protons and 6 neutrons)

  5. Ion • An atom that is positively charged or negatively charged • Anion have gained electrons (-); has more electrons relative to the number of protons (+) • Cation has lost electrons (-); has fewer electrons relative to the number of protons (+) • The electrical attraction of ions will cause an ionic bond to form between oppositely charged ions. • Na+ + Cl- = NaCl (halite)

  6. Compounds • Mixing of two or more chemical elements in particular proportions that have distinctive physical properties • Elements will bond because of electrical attraction, forming ionic bonds, or the atoms may share electrons, formingcovalent bonds

  7. MINERALS • Naturally occurring • Inorganic • Solid element or compound • Definite chemical composition • Regular internal crystal structure • Identified by recognizing different physical properties

  8. Figure 2.3A

  9. Figure 2.3B

  10. Identifying Minerals • The two fundamental characteristics of a mineral are its chemical composition and its crystal structure • Analyze the mineral composition • Technology based • Measure crystal structure and symmetry • Technology based • Observe and measure physical and special properties • Easy for humans to see and recognize

  11. Mineral Physical Properties • Color • Hardness • Cleavage • Luster • Density • Crystalline Form

  12. Mineral CompositionSilicate Group • Silicate group – variety of compounds based on silicon and oxygen • Quarts – glass manufacturing • Feldspar – ceramic manufacturing • Mica • Muscovite (white mica) • Biotite (dark mica) • Clays – used as drilling mud, in building materials, and as a soil modifier • Ferromagnesian silicates • Olivine – peridot (semiprecious gem) • Garnet - abrasives • Asbestos – industrial products

  13. Figure 2.6

  14. Figures 2.7 a and b

  15. Mineral CompositionNonsilicates • Carbonates – CO3 • Useful for building materials and manufacturing • Sulfates – SO4 • Useful for building materials • Sulfides – S • Host for many metallic ores (Pb, Cu, Zn, and others) • Oxides – any metal combined with oxygen • Iron and aluminum ores • Native elements – minerals composed of single element • Carbon as diamond and graphite • Cooper, gold, silver, or platinum

  16. Figures 2.2 c and d

  17. Figures 2.3 a and b

  18. Figure 2.4

  19. Figures 2.5 a and b

  20. Rocks – formed from Minerals • A solid aggregate of one or more minerals, or mineral materials • Consists of many mineral grains or crystals forming a solid mass • Each rock contains a record of its own history • Three broad categories • Igneous • Sedimentary • Metamorphic

  21. Igneous Rocks • Magma, at high enough temperatures, rocks and minerals can melt, and the natural hot, molten rock material is called magma • Silicates are the most common minerals, and magmas are thus rich in silica. Magmas also contain some dissolved water and gases, and include some solid crystals suspended in the melt • An igneous rock is a rock formed by the solidification and crystallization of a cooling magma

  22. Igneous Rocks • Rocks formed from hot, molten rock material – “fire” rocks • Usually composed of silicate minerals and some dissolved gases and water • Molten materials are very hot • Plutonic rocks form if magma does not flow onto surface; coarse crystals will grow • Volcanic rocks form if magma flows onto surface as lava; glass often forms

  23. Figures 2.10 a and b

  24. Igneous Rocks • Granite is the most widely known example of a plutonic rock, consisting of quartz, feldspars, and some ferromagnesian minerals or other silicates • Granites show the characteristic of a plutonic rock: the coarse and interlocking crystals • Lava, a magma that flows out on the earth’s surface while still wholly or partly molten • Volcanic, an igneous rock formed at or close to the earth’s surface • Basalt, the most common volcanic rock, rich in ferromagnesian minerals and feldspar

  25. Weathering of Rocks • Chemical weathering • Physical weathering • Sediments • Ions for cements

  26. Sedimentary Rocks • Sediments are produced by weathering of pre-existing rocks and minerals • Sediments are loose, unconsolidated accumulations of mineral or rock particles • Sediments are eroded, transported, and deposited in many sedimentary environments • The sediments will be buried and experience lithification • Lithificationinvolves compacting the sediments with burial and cementation of the sediments forming a sedimentary rock

  27. Sedimentary Rocks • Gravity plays a role in the formation of all sedimentary rocks. • Layering is a very common feature of sedimentary rocks and is used to identify the origins of sedimentary rocks. • Sedimentary rocks can yield information about the settings in which the sediments were deposited. • Sedimentary rocks are formed at or near the earth’s surface and at temperatures close to ordinary surface temperatures.

  28. Types of Sedimentary Rocks • Clastic sedimentary rocks • Formed by the lithification of mechanically broken up pieces of rocks and minerals • Grain sizes range from boulder, gravel, sand, silt, and mud • Grains are continually broken down in size and shape until deposited • Once deposited these clastic particles a cemented • Chemical sedimentary rocks • Chemical process occur in water bodies such as lakes, seas, or oceans • Minerals precipitate from the water form thick deposits • Examples: Halite, Calcite, and Gypsum

  29. Figures 2.11 Sedimentary Rocks

  30. Figures 2.11 Sedimentary Rocks

  31. Metamorphic Rocks • “Changed form” rock • Rock formed from pre-existing rock or minerals • Heat, pressure, and chemical active fluids cause changes in rock • Heat increases as a rock is buried or is close to a magma chamber • Pressure increases with burial or collision between moving continents • Fluids become heated and circulate with burial or with location near a magma chamber

  32. Metamorphic Rocks • The temperatures required to form metamorphic rocks are below magmatic temperatures • Significant changes can occur in a rock at temperatures well below melting • Temperature and pressure can cause the minerals in the rock to recrystallize • Pressure may cause the rock to be deformed • The sources of elevated temperatures of metamorphism: burial, magma, mountain-building, and plate tectonic movement • The sources of elevated pressures of metamorphism: burial, mountain-building, and plate tectonic movement

  33. Types of Metamorphism • Contact metamorphism – localized metamorphism of rocks adjacent to a magma chamber • Regional metamorphism – large scale stressing and heating of a rock by deep burial or continental plates moving and colliding

  34. Common Metamorphic Rocks • Any kind of preexisting rock (another rock) can be metamorphosed • Foliation: when a rock is subjected to directed stress, its minerals form elongated/platy crystals and line up parallel to each other • Metamorphic rocks without foliation do not directed stress • Marble is metamorphosed limestone • Quartzite is metamorphosed quartz-rich sandstone • Metamorphic rocks with foliation show directed stress or pressure • Slate – low grade foliated metamorphic rock • Schist and Gneiss (nice) – high grade metamorphic rocks

  35. Figures 2.12 Metamorphic rocks have undergone mineralogical, chemical, and/or structural change

  36. Figures 2.12 Metamorphic rocks have undergone mineralogical, chemical, and/or structural change

  37. The Rock Cycle • Three rock groups on the basis of their mode of origin: igneous, sedimentary, and metamorphic • Shows the interrelationships among the three rock types • Rocks of any type can be transformed into rocks of another type or into another distinct rock of the same general type through the geologic processes • Rocks are continually being changed by geological processes

  38. The Rock Cycle • Earth as a system: the rock cycle • Magma, a molten material formed inside Earth • Crystallization, magma cools and solidifies • Igneous rock, formed by “fire” underneath • Weathering, transportation, and deposition • Sediment • Lithification • Sedimentary rock • Metamorphism • Metamorphic rock • Melting • Magma

  39. The Rock Cycle • Earth as a system: the rock cycle • Full cycle does not always take place due to "shortcuts" or interruptions • e.g., Sedimentary rock melts • e.g., Igneous rock is metamorphosed • e.g., Sedimentary rock is weathered • e.g., Metamorphic rock weathers • Through time, geologic processes acting on older rocks change them into new and different ones so that, in a sense, all kinds of rocks are interrelated

  40. Fig. 2.13 The Rock Cycle

  41. The Rock Cycle • The Essence of the Rock Cycle • Igneous rocks, formed from magma • Sedimentary rocks, formed from low-temperature accumulations of particles or by precipitation from solution • Metamorphic rocks, formed from preexisting rocks through the change of temperature and pressure • Geologic processes working on old rocks change the old rocks into new and different ones, and thus all kinds of rocks are interrelated in a sense

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