Rocks and Minerals A First Look Chapter 2 Rocks and Minerals A First Look 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 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

Figure 2.1 Schematic drawing of atomic structure

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)

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)

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, forming covalent bonds

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

Figure 2.3A

Figure 2.3B

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 Observe and measure physical and special properties Easy for humans to see and recognize

Mineral Physical Properties Color Hardness Cleavage Luster Density Crystalline Form

Mineral Composition Silicate 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

Figure 2.6

Figures 2.7 a and b

Mineral Composition Nonsilicates 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

Figures 2.2 c and d

Figures 2.3 a and b

Figure 2.4

Figures 2.5 a and b

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

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

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

Figures 2.10 a and b

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

Weathering of Rocks Chemical weathering Physical weathering Sediments Ions for cements

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 Lithification involves compacting the sediments with burial and cementation of the sediments forming a sedimentary rock

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.

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

Figures 2.11 Sedimentary Rocks

Figures 2.11 Sedimentary Rocks

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

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

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

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

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

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

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

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

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

Fig. 2.13 The Rock Cycle

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