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Minerals Objectives • Define a mineral as an Earth material • Define physical properties that characterize minerals • Use physical properties to identify common rock-forming minerals Objectives • Define a mineral as an Earth material • Define physical properties that characterize minerals • Use physical properties to identify common rock-forming minerals Minerals • Comprise 99% of Earth’s crust • Basic geologic material of the Earth Table salt, halite What is a Mineral? • • • • Naturally occurring Made by non-human processes Crystalline solid Have a specific chemical composition Inorganic What is a Mineral? • • • • There is a repeatable Naturally occurring and orderly structure, Crystalline solid which forms a solid. Have a specific chemical composition Inorganic What is a Mineral? • • • • Naturally occurring Crystalline solid Have a specific chemical composition Inorganic Molecular composition expressed using a chemical formula may allow for some unknowns What is a Mineral? • • • • Naturally occurring Crystalline solid Have a specific chemical composition Inorganic Formed by Earth processes, rather than biological processes Source material may be derived from biological processes, such as shells How do minerals form? • A process called Crystallization: Atoms come together in the proper chemical proportions and ordered threedimensional arrangement and grow a solid from gas or liquid Minerals are the building blocks of most crustal rocks • There are about 9 elements found in large • • abundance in Earth’s crust (Oxygen, Silica, Aluminum, Iron, Calcium, Sodium, Potassium, Magnesium, Titanium) Leading to the 30 most commonly encountered rock-forming minerals Although there are thousands of known minerals geologists commonly encounter only about 30 of them… It is important to be able to identify common rock-forming minerals in order to then be able to identify rocks in the field Remember, there is a huge difference between minerals and rocks Next slide shows an example of common rock-forming minerals producing a granite rock Orthoclase feldspar Quartz Biotite Plagioclase feldspar Plagioclase feldspar Orthoclase feldspar Rocks are naturally occurring aggregates of minerals. Biotite Quartz Granite Some common rock-forming minerals Igneous Rocks Quartz Feldspar Mica Pyroxene(Augite) Amphibole Olivine Sedimentary Rocks Quartz Feldspar Clay minerals Calcite Dolomite Gypsum Halite Metamorphic Rocks Quartz Feldspar Mica Garnet Pyroxene Objectives of Lab Exercise • Define a mineral as an Earth material • Define physical properties that characterize minerals • Use physical properties to identify common rock-forming minerals Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Resistance to abrasion Reflects strength of chemical bonds between atoms Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Mineral Mohs Hardness Talc 1 Gypsum 2 2.5 3 4 5 5.5 6 6.5 7 8 9 10 Calcite Fluorite Apatite Orthoclase Quartz Topaz Corundum Diamond Common Object Fingernail Copper Glass or knife blade Steel file (varies) Mineral Identification Properties • • • • • • • • Geometric shape of Hardness crystals when grown in Crystal Form an unconfined space Cleavage Reflects geometric Fracture arrangement of the Color atoms Streak Single crystals --> cubes, prisms, rhombohedrons, dodecahedrons, tabular, acicular Luster Crystal masses --> granular masses, crystalline masses, botryoidal masses Others Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others How minerals break (determined by observation, not breaking) Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Breakage in a planar fashion, broken surfaces are flat Described according to how many different “directions” of cleavage there are and how “good” the cleavage is (I.e., how smooth the surface is) Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Reflects weaker molecular cohesion along cleavage planes Can be confused with crystal form Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others mica: 1 cleavage plane Grotzinger et al. © 2007 by W.H. Freeman & Company Grotzinger et al. © 2007 by W.H. Freeman & Company Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Grotzinger et al. © 2007 by W.H. Freeman & Company orthoclase feldspar: 2 cleavage planes Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Breakage in a nonplanar fashion, broken surfaces are: Rough --> “irregular fracture” Curved or Rounded --> “conchoidal fracture” Pointed --> “hackly fracture” Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Conchoidal Fracture Oregon Obsidian © Public Domain http://en.wikipedia.org Obsidian Arrowhead © Public Domain http://en.wikipedia.org Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Pigment of “fresh” mineral surface in white light “fresh” --> clean and untarnished It is highly variable and unreliable alone Mineral Identification Properties COLOR is highly variable and unreliable alone amethyst milky quartz ©1995-2006 by Amethyst Galleries, Inc. rose quartz © 1998-2003 Gem & Mineral Miners, Inc.® © StoneTrust, Inc. jasper © 1998-2003 Gem & Mineral Miners, Inc.® citrine rock crystal © 1998-2003 Gem & Mineral Miners, Inc.® © 1998-2003 Gem & Mineral Miners, Inc.® Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Color of mineral in powdered form on an unglazed porcelain plate (“streak plate”) More reliable than color Grotzinger et al. © 2007 by W.H. Freeman & Company Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others How a fresh mineral surface reflects light: “Metallic” - looks like a shiny metal (opaque, shiny, metallic colors) “Submetallic” - looks like a duller metal “Nonmetallic” - all others, e.g., glassy or vitreous, dull or earthy, pearly, silky, waxy, resinous, adamantine Mineral Identification Properties Pyrite * Metallic * Vitreous * Resinous ©1995-2006 by Amethyst Galleries, Inc. Quartz * Greasy * Pearly * Silky USGS * Adamantine Sphalerite ©2003, Alan Plante, Donald Peck, & David Von Bargen Mineral Identification Properties * Metallic Nepheline and cancrinite (yellow) * Vitreous Stellerite * Resinous * Greasy * Pearly * Silky * Adamantine Diamond Gypsum (variety satin spar) all images ©2003, Alan Plante, Donald Peck, & David Von Bargen Mineral Identification Properties * Metallic * Vitreous * Resinous * Greasy * Pearly * Silky * Adamantine * Earthy * Dull Limonite StoneTrust Inc. Mineral Identification Properties * Metallic * Vitreous * Resinous * Greasy * Pearly * Silky * Adamantine * Earthy * Dull Hematite NOAA Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Striations - tiny, parallel grooves on a cleavage face. These form due to crystal growth along closely parallel surfaces Norris W. Jones and Charles E. Jones © McGraw-Hill Striations Calcium Plagioclase Feldspar Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Specific Gravity - “heftiness” weight of volume of mineral weight of same volume of water Mineral Identification Properties • • • • • • • • Hardness Crystal Form Cleavage Fracture Color Streak Luster Others Tests only for Specific Minerals: - Taste - Smell - Magnetism - Reaction to Acid Mineral Identification Properties Sulfur smells like rotten eggs Halite tastes like salt Grotzinger et al. © 2007 by W.H. Freeman & Company ©1995-2006 by Amethyst Galleries, Inc. Calcite reacts with HCl strongly Dolomite reacts with HCl weakly Magnetite strongly magnetic © Lou Perloff / Photo Atlas of Minerals © Lou Perloff / Photo Atlas of Minerals © 2006 Robert James / YourGemologist.com Objectives of Lab Exercise • Define a mineral as an Earth material • Define physical properties that characterize minerals • Use physical properties to identify common rock-forming minerals - this lab focuses on field tests (simple physical tests to determine the mineral)