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This 11 page Class Notes was uploaded by Ashleigh Provance on Wednesday February 24, 2016. The Class Notes belongs to 105 at University of Mississippi taught by Amanda Patterson in Spring 2016. Since its upload, it has received 22 views. For similar materials see Geol Web in Geology at University of Mississippi.
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Date Created: 02/24/16
Chapter 3: Minerals and Rocks Minerals: basic building blocks of earth Made up of several elements or single element—ex: gold, ice or compound ▯ To Be a mineral: Naturally occurring Inorganic Solid Characteristic chemical formula Characteristic crystalline structure ▯ ▯ Atoms of the same element with a different number of neutrons are known as ____. isotopes ▯ ▯ Crystalline Structure Of minerals: Crystalline: having orderly, regular repeating geometric pattern of atoms Unit cell: smallest repeating unit of those atoms o Dictate what mineral will look like based on arrangement— crystal form/habit ▯ -unit cells stick together—form the mineral ex: table salt(haylight)—cubic arrangement from mineral ▯ ▯ atoms are held together by chemical bonding ▯ Types of Bonds: Covalent- atoms that share electrons—very strong bond (hard to break) o Durable minerals-----diamond Ionic- attraction between + and – charged ions o Soluble minerals, chemically active and mobile ----halite(sodium+chlorine) o Ionic bonds- attraction rom an anion and a cation Van der waals-weak attraction between chains or sheets of ions o Graphite- pencil lead—soft greasy feel Metallic- electrons are shared by all atoms and can flow o Metallic minerals- results in malleability and ability to conduct electric current ▯ Minerals: 4000 known hand specimen identification: ID by appearance and physical properties ▯ ▯ Physical Properties: (Mohs Scale) Hardness- determine with common tools that have known harnesses’ (1:talc-10:diamond) fracture- breaking of a mineral--- pattern to way it breaks o appearance of glass- concoital fracture(quartz) cleavage- when a mineral tends to break along certain planes of weakness o pieces seem to have general shape—3 different planes the pieces are breaking along cleavage directions- 1(flat sheets)—muscovite 2 at 90 degrees- rectangle with cross section – feldspar 3 cleavage directions—calcite luster- does it have a metallic or non metallic luster o silvery gray(glena)- metallic luster o lighter color—glassy/non metallic- quartz streak- color of powder form of mineral o reddish brown double refraction(optical property)- light passes through, you can see through calcite crystal form/habit- reflection of way the atoms bond together within the mineral—appearance of mineral based on unit cell combines( how it forms) o halite-cubic crystal( table salt) o quartz—hexagonal crystal reaction with acid o calcite reacts with hydrochloric acid magnetism- some minerals are magnetic ▯ ▯ Common Mineral Classes/Groups: Silicates- 98% of mineral mass of earth’s crust—largest class o 45% of crust is oxygen, 27% is silicon o silicon and oxygen combine with other elements to make up most silicate minerals o all have silicate oxy tetrahedral- 1 atom of silicon, 4 oxygen atoms—forms triangle o different silicate minerals—chain or sheets of silicate oxy tetrahedral+ different elements Quartz- SiO2—mineral in crust, hardest mineral and has conchoidal fracture(looks like broken glass), variety of colors( light- quartz) determined by impurities Ex: amethyst(purple)- smokey quartz(greyish) MOST COMMON MINERAL IN EARTH’s Crust Feldspars- most abundant on surface of earth Alkali(sodium rich) +plagioclase(calcium rich) Micas- sheets of Si-O tetrahedral Ex: muscovite(black +transparent) and biotite- darker Ferromagnesian silicate( dark minerals In most rocks Will contain iron or magnesium Tend to be weathered easily( oxidize, produce weak rocks, form clays and soluble salts) ▯ - common in igneous rocks Carbonates o Calcite is most important environmentally o Chemical weathering of carbonate bearing rocks produces caverns and sinkholes Water can come into contact with that rock and dissolve to form caverns Oxides o Metal atoms combines with oxygen o Includes ores( hematite(fe) and bauxite(al) especially of iron and aluminum Sulfide o Metal ions combines with sulfur o Pyrite- when it comes in contact with air and oxygen or water —can oxidize and form sulfuric acid - and other ore minerals Native Elements o Minerals composed of single elements gold, silver, copper, diamonds, graphite PART TWO OF LECTURE: ▯ ▯ Rocks: An aggregate of one or more minerals Classified according to how they form in rock cycle ▯ ▯ The Rock Cycle: pg 86 worldwide rock recycling system linking subsurface and surface processes produces three main groups of rocks, depending on the environment crystallization of molten rock produces igneous rocks, o rocks near the surface break down chemically or physically and weather to form sediments—these sediments are accumulated layers that form sedimentary rocks o sedimentary rocks break down by heat or pressure to form metamorphic rocks ▯ Plate Tectonics: Several environments for rock formations Specific rock processes occur at different plate boundaries Types: igneous- crystallization of molten rock(magma>lava) sedimentary- accumulated layers of sediment from preexisting rocks( been weathered, eroded—over time form a sedimentary rocks—existing rocks can become dissolved or it could be from pieces of rock to form a rock) metamorphic- preexisting rocks that can be altered in form and mineral makeup by heat, pressure, or fluids ▯ ▯ Rock Laws: 1) cross cutting relationships o A rock is younger than any other rock it cuts 2) Original Horizontality( rocks were originally horizontal) o sedimentary layers are nearly horizontal when deposited 3) superposition o the oldest layers of sediments are on bottom and youngest layers on top are a series of layers that have not been overturned ▯ ▯ Igneous Rocks: Crystallized from molten rock(magma) Rate at which it cools- influences igneous rock ▯ ▯ What makes up the rock, how quickly does it cool? ▯ Intrusive igneous Rocks: Cool slowly and crystallize well below the surface of the earth o COOLS INSIDE THE EARTH’S INTERIOR Individual mineral grains can be seen with the naked eye INCLUSIONS- Pieces of surrounding rock incorporated into crystallizing magma Batholiths- really big masses of igneous rock ▯ ▯ Why does magma rise and intrude other rocks? Once formed, a mass of magma is hotter and less dense than surrounding rocks o Less dense(boyant)—magma body rises into crust and rises as high as it can until it is a similar density to the surrounding rocks ▯ ▯ Extrusive Igneous rocks: Crystallize at surface of earth Form from lava or pyroclastic debris Fine grained because they cool rapidly Magma is out of interior of earth( lava or volcanic eruption) ▯ ▯ Magma- beneath surface; lava- reaches surface ▯ ▯ Igneous Rocks and the Environment: Intrusive rocks are resistant to weathering—form good foundation materials Some weaknesses- lava tubes—was flowing now void beneath the surface o Lava flows is cooled- columnar jointing(looks like columns)— weakness Building large structures—do a field investigation to make sure rocks are good ▯ ▯ Sedimentary Rocks : 75% of rocks exposed at Earth’s surface form as a result of other rocks weathering ▯ ▯ 2 types: detrital/clastic—formed from broken pieces of preexisting rocks chemical- formed when fluids interact with preexisting rocks and dissolve out their ions—then they precipitate out of the solution to form a rock o chemical or biochemical processes cause minerals to form from substances dissolved in water ▯ ▯ Diagenesis: changes in sediments as a result of burial and fluid passage ▯ ▯ Sedimentary process: 1. sediment is delivered to a sedimentary basin ( sediments accumulate) 2. sediment is deposited in layers( carried by wind etc.)—deposited horizontally 3. basin sinks or sea level rises, several kilometers of sedimentary rocks can be deposited—huge thick layer 4. Pressure from overlying material, water circulating through material, or other precipitation of minerals from pore waters cements the rocks Classifying Sedimentary Rocks: ▯ Detrital—grain size Size of sediments- tiny(shale)---- pebbles, gravel(conglomerate) ▯ Chemical- chemical composition Halite( salt)----- limestone(calcite), most abundant of chemical sedimentary rocks, composed of calcite ▯ ▯ Sedimentary rocks and environmental concerns: Shale, mudstone, and siltstone are very weak Limestone generally is not well suited for human use—weathering characteristics Cementation can be weak—can crumble overtime ▯ ▯ Metamorphic Rocks: Rocks changed by heat, pressure, and chemically active fluids ▯ ▯ Types: Foliated- mineral grains are aligned in parallel layering or banding- producing a rock cleavage or foliation o Slate- fine particles(foliation forms)—breaks off into sheets to form mica crystals o Schists- particles(mica crystals) become large and rock develops foliation o Gneiss- mica crystals are transformed to feldspar- banding of light and dark minerals Nonfoliated o No alignment of mineral grains o Ex: marble( made of calcite)—(metamorphosed limestone), quartzite(metamorphosed sandstone) ▯ ▯ Metamorphic Rocks and the Environment: As foundation materials o Slate is good o Schist is poor- too soft of minerals o Gneiss is suitable strength o Foliation planes are potential weakness ▯ ▯ St Francis Dam Case History: Dam in san francisquito canyon near Saugus California failed o Foliation planes for metamorphic rock were parallel to the wall o Rocks disintegrated and became wet- contact between metamorphic and sedimentary rocks Sliding of sedimentary rock and leakage of water along planes—destroyed concrete and precipitated failure ▯ ▯ Rock Structures: ▯ 1. Fractures- joints: no displacement along fracture faults: displacement along fracture--- movement along the crack ▯ A: Problems with fractures Act as pathways for fluids Zones of weaknesses Fracture is subject to weathering—widens and weakens it o Crack will become wider and weaker ▯ 2. Folds form when layers are shortened by compression o anticline-upward o syncline-downward ▯ 3. unconformities break in geologic record—gap in time something happened in past—don’t see evidence of it—something is missing form boundary between contrasting rock types o nonconformity- forms between older igneous rocks or metamorphic rocks and younger sedimentary rocks o angular unconformity- younger sedimentary rocks are located upon an erosion surface, below which older sedimentary rocks are tilted or folded o disconformity- erosion surface between parallel layers of sedimentary rocks o
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