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Good Web Sites about Minerals: • http://galaxy.einet.net/images/ge ms/gems-icons.html • Smithsonian Gem and Mineral Collection -- lots of spectacular mineral pictures and good information The Rock Cycle A model that describes all the crustal processes by which rock is formed, modified, transported, decomposed, and reformed. N.Lindsley-Griffin, 1999 Rocks are made up of minerals N. Lindsley-Griffin, 1999 What is a Mineral? • Occurs naturally • Not previously living (inorganic) • Solid • Definite chemical composition • Orderly internal atomic arrangement N. Lindsley-Griffin, 1998 Ivory, bone, seashells, coral, petrified wood, and other previously living things… are NOT minerals N. Lindsley-Griffin, 1998 Minerals are made up of atoms Atomic number = number of protons; gives atoms their distinctive characteristics. Atomic mass = protons plus neutrons N. Lindsley-Griffin, 2000 Ions combine to form compounds Here, the Li atom loses an electron to become a + positively charged cation. The F atom gains an electron to become a negatively charged anion. Positive and negative charges attract each other to form an IONIC BOND N. Lindsley-Griffin, 1999 Covalent Bonding -- atoms share electrons to form a strong bond. Diamond Diamond and graphite are the same chemical composition (Carbon) but exhibit very different internal structures. Graphite N. Lindsley-Griffin, 1999 Van der Waals Bonding -- a weak bond caused by a weak secondary attraction between molecules. Graphite N. Lindsley-Griffin, 1999 Orderly array of atoms in the mineral Galena: large atoms - sulfur, small - lead As seen with a scanning-tunneling microscope N. Lindsley-Griffin, 1999 The orderly arrangement of atoms in Galena controls its physical properties. Error in textbook on Figure 2.7: Sulfur atoms, not “oxygen” Sulfur atom N. Lindsley-Griffin, 1999 Crystal Interfacial Angles Interfacial angles of a given mineral are constant for all crystals The faces of quartz always form 120-degree angles © Houghton Mifflin 1998; Lindsley 2000 Crystal Interfacial Angles • Even when the crystals are different sizes, angles between equivalent faces are the same • For different minerals, angles are different. 3 2 4 4 3 1 2 Quartz N. Lindsley-Griffin, 1999 1 Habit Habit - distinctive shape of the way the mineral commonly (habitually) appears N.Lindsley-Griffin, 1999 Concentric shells -- malachite Habit N. Lindsley-Griffin, 1998 Crystal shape and Habit result from internal atomic structure N. Lindsley-Griffin, 1998 Cleavage - tendency to break along planes of weak bonds N.Lindsley-Griffin, 1998 Mica cleaves along planes of the weakest bonds N. Lindsley-Griffin, 1998 Fracture describes how a mineral breaks on an irregular surface rather than along cleavage planes Types of fracture: Smooth Rough Splintery Conchoidal N. Lindsley-Griffin, 1998 Hardness Hardness -- the resistance to being scratched Mohs scale measures relative hardness, the ability of one mineral to scratch another Diamond Corundum Topaz Quartz Feldspar Apatite Fluorite Calcite Gypsum Talc 10 9 8 7 6 5 4 3 2 1 Steel file Glass (6.5) (5.5- 6) Copper penny Fingernail (3.0) (2.5) Mohs hardness scale: 1 = softest mineral; 10 = hardest © Houghton Mifflin 1998; Lindsley 2000 The 10 minerals of Mohs relative hardness scale 3 Calcite 1 Talc 4 Fluorite 2 Gypsum 9 Corundum 6 Feldspar N. Lindsley-Griffin, 1999 5 Apatite 7 Quartz 8 Topaz 10 Diamond Luster Luster - the appearance of a mineral in reflected light Types of luster: Metallic Nonmetallic Pearly Vitreous Resinous Silky Dull Earthy Metallic luster of pyrite © Houghton Mifflin; N. Lindsley-Griffin, 1998. Earthy luster of limonite Metallic Luster is characteristic of ore minerals and others that contain metal cations. N. Lindsley-Griffin, 1998 Resinous luster in sphalerite Pearly luster in talc N. Lindsley-Griffin, 1999 Color is useful in recognizing some minerals, but not all N. Lindsley-Griffin, 1998 Color adds value to gems N. Lindsley-Griffin, 1999 Streak, the color of the mineral’s powder, may be more useful than color in identifying a mineral N. Lindsley-Griffin, 1998 Structure of Silicate Minerals Most rocks consist of silicate minerals. The silicon-oxygen tetrahedron is the building block of silicate minerals Four oxygen ions surround a much smaller silicon ion © Houghton Mifflin 1998; Lindsley, 2000 The silicate tetrahedron consists of 4 large oxygen atoms around a smaller silicon atom Expanded View N. Lindsley-Griffin, 1999 Two tetrahedrons link together by sharing an oxygen at one corner Silicate tetrahedrons can form chains, sheets, and three-dimensional nets by sharing their oxygen atoms. Each influences mineral properties. N. Lindsley-Grifin, 1999 Tetrahedral Linkages A. Isolated tetrahedra - Olivine B. Single chain - Pyroxene C. Double chain - Amphibole D. Sheets - Micas, clay, talc E. Framework - Quartz, feldspar © Houghton Mifflin 1998. All rights reserved Polymorphs are minerals with the same chemical composition, but different internal atomic structures N. Lindsley-Griffin, 1998 SUMMARY: PHYSICAL PROPERTIES of MINERALS Crystal Structure Crystal Form Interfacial Angles Habit Cleavage Fracture © Houghton Mifflin 1998; N. Lindsley-Griffin, 1999. All rights reserved Hardness Luster Color Streak Specific Gravity (Density)