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 Illinois Fluorite, photo by J. Carr

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 an element may not be the same; variable numbers of neutrons possible –Atomic Mass Number is the number of protons and neutrons in the element’s nucleus –Some isotopes have more neutrons 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 has 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 –Technology based 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  Quartz – glass manufacturing  Feldspar – ceramic manufacturing  Mica Muscovite (white mica) Biotite (black mica)  Clays – used as drilling mud, in building materials, and as a soil modifier Ferromagnesian silicates  Olivine – peridot (semiprecious gem)  Garnet – abrasives; semiprecious gems  Amphibole – industrial products

Figures 2.7 a and b

Mineral Composition Nonsilicates Carbonates – CO 3 –Useful for building materials and manufacturing Sulfates – SO 4 –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 –Copper, gold, silver, or platinum

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 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; iron content is variable and this variability is the basis for igneous rock classification 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 Usually composed of silicate minerals and some dissolved gases and water Molten materials are very hot –Plutonic rocks form if magma cools inside earth’s crust (does not flow onto surface); coarse crystals will grow –Volcanic rocks form if magma flows onto surface as lava; glass often forms

Igneous Rocks *Know this chart Felsic; low iron light toned Intermediate Mafic; high iron dark toned Ultramafic Volcanic; extrusive; aphanitic RhyoliteAndesiteBasaltEclogite Plutonic; intrusive; phaneritic GraniteDioriteGabbroPeridotite

Weathering of Rocks Chemical weathering Physical weathering Creates Sediments Ions for cements

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

Sedimentary Rock FACTS: 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. They yield information about the settings or environment in which the sediments were deposited. They are formed at or near the earth’s surface and at temperatures close to ordinary surface temperatures.

2 Types of Sedimentary Rocks 1.Clastic sedimentary rocks –Formed by the lithification of mechanically weathered pieces of rocks and minerals (fragments) Grain sizes range from boulder, gravel, sand, silt, and mud –Once deposited these clastic particles a cemented ie. Conglomerate, sandstone… 2.Chemical sedimentary rocks –Chemical process occur in water bodies such as lakes, seas, or oceans (ie. evaporation) –Minerals precipitate from the water and form thick deposits Examples: Halite, Calcite, and Gypsum

Figures 2.11 Sedimentary Rocks

Metamorphic Rocks “Changed form” rock Rock formed from pre-existing rock or minerals Heat, pressure, and chemically 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 Rock Changes 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 Sources of elevated temperatures of metamorphism: burial, magma, mountain-building, and plate tectonic movement 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 pre-existing 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 1. Nonfoliated Rocks do not show directed stress –Marble is metamorphosed limestone –Quartzite is metamorphosed quartz-rich sandstone 2. Foliated Rocks show directed stress or pressure –Slate is low grade foliated metamorphic rock –Schist and Gneiss is high grade metamorphic rocks

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

The Rock Cycle Rocks grouped on the basis of their mode of origin: igneous, sedimentary, and metamorphic Shows the interrelationships between 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 Full cycle Magma, a molten material formed inside Earth Crystallization, magma cools and solidifies Igneous rock: formed by “fire” underneath Weathering, transportation, and deposition (sediment formation ) Lithification Sedimentary rock Metamorphism (heat and pressure) Metamorphic rock Melting Magma Forms

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 The Rock Cycle