Geo 101 1st Edition Lecture 4 Outline of Last Lecture 1 Theory of Plate Tectonics 2 Continental Drift 3 Wegner s Hypothesis 4 Continental Drift Renewed Interest 5 Earth s Magnetic Field 6 Continental Drift Paleomagetism 7 A Scientific Revolution Begins a Seafloor Mapping 8 Plate Tectonics The New Paradigm Outline of Current Lecture 1 Minerals Building blocks of rocks 2 What is a mineral 3 Composition of Minerals 4 Chemistry Refresher a Structure of Atom b Chemical Bonding i Ionic ii Covalent iii Metallic iv Van Der Walls 5 Structure of Minerals 6 How do we Identify Minerals a Diagnostic Properties i Crystal Form Shape ii Luster iii Color iv Streak v Harness vi Cleavage vii Fracture viii Specific Gravity ix Other Properties 7 Mineral groups 8 Categories of Silicate Minerals 9 Non Silicate Minerals These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Current Lecture Patterns in Nature Minerals Minerals Building blocks of rocks Minerals are NOT rocks Rocks are made up of minerals What is a mineral By definition a mineral is o Naturally occurring o Homogeneous o Define chemical composition o Inorganic crystalline solid Minerals have an ordered internal arrangement of atoms Composition of Minerals Elements o Building blocks of minerals i e minerals one or more elements o Over 100 different elements Atoms o Smallest particles of matter o Building blocks of elements Chemistry Refresher Structure of Atom o Nucleus Protons Neutrons no charge o Electrons Surround nucleus Located in energy levels called shells each shell generally has room to hold 8 electrons Shells are most stable when they are filled What defines an element An element is chemically defined by the number of protons o Different number of neutrons isotope ex C 14 and C 12 o Different number of electrons ion Cation positive charge Anion negative charge Chemical Bonding Combining 2 or more elements to form a compound e g minerals 1 Ionic bonding o Atoms gain or lose outermost electrons creating ions o Ionic compounds have an orderly arrangement of oppositely charged ions opposites attract o Makes them electronically stable or neutral 2 Covalent Bonding o Atoms share electrons to achieve electrical neutrality try to fill their outer electron shells o Stronger Ionic Bond 3 Metallic bonds o Electrons migrate among atoms good conductivity Ex copper gold Makes really good conductors Most things are metals 4 Van Der Waals Bonds o Weak attractive force between electrically neutral atoms stacking interaction Ex graphite REVIEW QUESTIONS Which of the following is NOT a characteristic defining a mineral Random internal structure What type of bonding occurs when atoms share electrons Covalent Which type of chemical bond is the weakest Van Der Waals Structure of Minerals Minerals orderly array of atoms bonded to form a crystalline structure Different atoms will pack into different arrangements o Tetrahedron o Octahedron o Cube o Cuboctahedron o ETC Orderly arrangement givens minerals symmetry Polymorphis o Minerals with the same composition but different crystalline structures Ex diamond and graphite are polymorphis of carbon How do we identify minerals Primary Diagnostic properties o Determined by observation or performing simple tests o Several physical properties are used to identify hand samples of minerals Diagnostic properties Crystal Form Shape o External expression of mineral s internal structure i e how atoms are arranged Luster o Appearance in reflected light o 2 major categories Metallic looks like metal Nonmetallic Color o Generally unreliable for mineral ID variable due to impurities in mineral chemistry o Colorations of minerals produce gemstone o Most unreliable o Corundum Blue sapphire if you mix iron Red rubies if you mix chromium So sapphires and rubies are the same thing but mixed with something else o Beryl Green emeralds chromium Blue aquamarine iron Again same thing Streak o Color of a mineral in its powdered form o Obtained by scratching the mineral on a porcelain plate o Can be different from color because in powder form the effect of impurities is reduced Hardness o Resistance of a mineral to abrasion or scratching o All minerals are compared to a standard scale called the Mohs hardness scale Goes from 1 10 Low number is softer Diamond is a 10 Tale is a 1 Measuring hardness of minerals against other minerals Cleavage o Tendency to break along plates of Weak bonding o Produces flat shiny surfaces Fracture o Absence of cleavage when a mineral is broken Specific Gravity o Weight of mineral divided by the weight of an equal volume of water o Average 2 7 g cm3 Other Properties o Magnetism Magnetite o Reaction to hydrochloric acid Dolomite o Double refraction shadow effect Calcite o Taste Halite o Smell Sulfur REVIEW QUESTIONS Which diagnostic property is the least reliable Color impurities Streak of a mineral will always be the same as its color False Polymorphs have the same composition but different crystalline structure True Minerals Nearly 4000 different minerals Rock forming minerals o Only a few dozen members o Made of the most common elements in the Earth s crust Mineral Groups Silicates SiO4 o Most important mineral group o Compromise most rock forming minerals o Very abundant due to large percentage of silicon and oxygen in the Earth s crust o Silicon Oxygen tetrahedron fundamental building block o Four oxygen ions surrounding a smaller silicon ion Tetrahedral forms By combining the SiO4tetrahedra together in different ways we can make different minerals Categories of Silicate SiO4 Minerals Mafic o o o o Felsic o o o o Simpler SiO4 structure Dark colored more dense Contain iron and magnesium EX Olivine Biotite Amphibole More complex SiO4 structure Light colored less dense No iron or magnesium EX Quartz Feldspar Muscovite Non Silicate Minerals Only 8 of the Earth s crust Many non silicate minerals have important economic value Examples o Hematite oxide mined for ion ore o Halite halide mined for salt o Sphalerite sulfide mined for zinc ore o Native copper mined o Carbonates mined for cement