Lecture Outlines Physical Geology, 14/e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plummer, Carlson & Hammersley

Atoms, Elements, and Minerals Physical Geology 14/e, Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Mineral – a naturally occurring, inorganic, crystalline solid that has a specific chemical composition. forms in the geosphere, hydrosphere, biosphere, and even the atmosphere consistent and recognizable physical and chemical properties Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Minerals

Element – a substance that cannot be broken down to other substances by ordinary chemical reactions Atom – the smallest unit of a substance that retains the properties of that element protons (+ charged) neutrons (0 net charge) electrons (- charged) Molecule – the smallest unit of a compound that retains the properties of that substance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atoms and elements

Protons and neutrons form the nucleus of an atom represents tiny fraction of the volume at the center of an atom, but nearly all of the mass Electrons orbit the nucleus in discrete shells or energy levels represent nearly all of the volume of an atom, but only a tiny fraction of the mass electrons = protons chemical reactions involve only outermost shell (valence) electrons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atomic structure

Isotopes – atoms of an element with different numbers of neutrons stable isotopes o retain all of their protons and neutrons through time o stable isotopes of oxygen can be used to track climate change over time unstable or radioactive isotopes o spontaneously lose proton(s) and/or neutron(s) from their nuclei over time Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. isotopes

Chemical bonding – controlled by outermost shell (valence) electrons elements will typically be reactive unless their valence shell is full Ions – atoms or groups of atoms with unequal numbers of protons and electrons, thus having a non-zero charge positive and negative ions are attracted to one another and may stick or chemically bond together Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical bonding

Ionic bonding – involves the transfer of valence electrons from one atom to another Covalent bonding – involves sharing of valence electrons among adjacent atoms Metallic bonding – electrons flow freely throughout metals; results in high electrical conductivity Ionic bonding of NaCl (sodium chloride) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical bonding

Common elements ~ 97% of the atoms in the crust are represented by 8 common elements: O, Si, Al, Fe, Ca, Na, K, Mg Common mineral types most minerals are silicates (Si + O) Minerals have crystalline structures regular 3-D arrangement of atoms Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Elements in the earth

Silicon-oxygen tetrahedra Strongly bonded silicate ion Basic structure for silicate minerals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Silicate structures

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Silicate structures Sharing of O atoms in tetrahedra the more shared O atoms per tetrahedra, the more complex the silicate structure o isolated tetrahedra (none shared) o chain silicates (2 shared) o double-chain silicates (alternating 2 and 3 shared) o sheet silicates (3 shared) o framework silicates (4 shared)

Carbonates – contains CO 3 in their structures (e.g., calcite - CaCO 3 ) Sulfates – contains SO 4 in their structures (e.g., gypsum - CaSO 4. 2H 2 O) Sulfides – contains S (but no O) in their structures (e.g., pyrite - FeS 2 ) Oxides – contains O, but not bonded to Si, C or S (e.g., hematite - Fe 2 O 3 ) Native elements – composed entirely of one element (e.g., diamond – C) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Non-Silicate minerals

Mineral criteria crystalline solid, atoms are arranged in a consistent and orderly geometric pattern naturally occurring geological processes specific chemical composition with some variation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. minerals

Rock-forming minerals > 4500 minerals identified ~ 20 form the majority of all rocks (rock-forming minerals) > 90% of Earth’s crust is composed of minerals from only 5 groups (feldspars, pyroxenes, amphiboles, micas, quartz) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. minerals

Ore minerals – minerals of commercial value most are non-silicates (primary source of metals) must be able to be extracted profitably to be considered current resources Gemstones prized for their beauty and (often) hardness may be commercially useful diamond, corundum, garnet, and quartz are used as abrasives Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. minerals

Color – visible hue of a mineral Streak – color left behind when mineral is scraped on unglazed porcelain Luster – manner in which light reflects off surface of a mineral Hardness – scratch-resistance Crystal form – external geometric form Physical and chemical properties of minerals are closely linked to their atomic structures and compositions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mineral properties

Cleavage – breakage along flat planes Fracture – irregular breakage Specific gravity – density relative to that of water Magnetism – attracted to magnet Chemical reaction – calcite fizzes in dilute HCl Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mineral properties

End of Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.