EAR101-M001-9/19&9/21 EAR 105 - M001
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This 7 page Class Notes was uploaded by Cara-Liesel Ransom on Friday September 30, 2016. The Class Notes belongs to EAR 105 - M001 at Syracuse University taught by C. Junium in Fall 2016. Since its upload, it has received 6 views.
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Date Created: 09/30/16
EAR101-M001 Monday9/19/16 ~Review~ 1. Convergent boundaries are where two plates collide 2. Subduction zones have unique features a. Accretionary prisms b. Volcanicarcs c. Large earthquakes Continental Lithosphere collisions create large mountain ranges like the Himalayas Subduction consumes ocean basins Ocean closure ends in continental collision o Continental crust is too buoyant to subduct. o Subduction ceasesand mountains are uplifted Transform Boundaries (sliding motion) Continental transforms – chop continental crust o Ex:The Sane Andrea Fault The earthquake magnitudes areoften smaller when transform boundaries shift past each other. Hotspots Plumes of deep mantle material independent of plates. o Notlinked toplate boundaries o Made of lowermantle mafic magmas o Burn through plates and add lines of volcanoesto them o Hotspots are fixed and the plates go over them. Ex:Hawaii. The hotspot is fixed and the plate goes over it.There is a hitch in its motion froma past shift in the tectonicplate overhead it. Driving Mechanisms What drives plate motion? o Old idea: plates are dragged atopa convecting mantle. Plate motions are much too complex. Convectiondoes occur; not the prime driving mechanism. The flowis what drives the motion of the plates. Modern thinking: two other forcesdrive plate motions. o Ridge-push: elevated MOR pushes lithosphere away. o Slab(the part that is going back down into the mantle)-pull: gravity pulls a subducting plate downward. o Convectionin the asthenosphere adds orsubtracts. How fastdoes a plate move? (2-20 cm/yr) Plate vectors are determined GPS measurements. o Global Positioning System (GPS) uses satellites. o Knowledge of plate motion is now accurateand precise. o None of them move atthe same speed. ~Andthat’s it for Plate Tectonics~ Minerals ~Canbe a dry subject,there is a lot ofchemistry involved.But what should be focusedonis that these minerals eventuallymake upthe rocks onthe planet, and eventually to the plate skin. ~ Why careabout minerals? Minerals are the building blocks of the planet. They have a solid economic value. Minerals are important to humans. o Industrial minerals: raw materials for manufacturing. o Ore minerals: sources of valuable metals o Gem minerals: attracthuman passions. o We have to know where they are, their purity... a geologist does this. If it is not grown, it is mined. What is a mineral? Minerals are formed by natural processes They are formed by geologic processes. o Solidification (“freezing”) froma melt (think cooling lava) o Precipitation froma dissolved state in afluid (water) Living organisms can createminerals. o Called biogenic minerals toemphasize this special origin Vertebrate bones (apatite) Oyster, mussel, and clam shells (aragonite) Other skeletal types Minerals are solids and found in nature You can make anything in the lab, but natural conditions dictate the range of elements that will be found together. Minerals have specific chemical compositions and a crystalline structure. Can be one or many elemtns o Gold (just one element) o Feldspars, Al, Si, O, with Ca, K, Na Can have ionic or covalentbond o NaCl, salt,ionic Minerals are inorganic Organic compounds have carbon and hydrogen bonds o Some minerals have carbon and hydrogen but not bonded together Minerals are ordered, repeatable arrangements of atomsthat formsolids. We describe this order as “crystalline” Crystals o Atoms are arranged in a periodic, repeating pattern of single units What exactly is a crystal? A single, continuous piece of crystalline solid. Typically bounded by flatsurfaces (crystal faces) Crystal facesgrow natural asthe mineral forms. Crystals are sometimes prized mineral specimens. Crystals have a specificgeometry and symmetry. Constancy of interfacialangles o The same mineral has the same crystal faces. o Adjacent facesoccurat the same angle to one another. Faces and angles reflect crystalline structure. Crystals have specific shapes (called form orhabit) Crystals comes in a variety of shapes Many descriptive terms describe crystal shape. What is inside acrystal? What you see on the outside, is repeated on the inside. Ordered atoms, like tiny balls packed tightly together. Held in placeby chemical bonds. The way atoms are packed defines the crystal structure. Physical properties (hardness, shape) depend upon: o Identity of atoms o Arrangement of atoms o Nature of atomicbonds The order is defined by bonding at the atomiclevel Minerals are based on units of atoms (like letters in aword) The units are called unit cells Wednesday 9/21/16 Minerals Cont. Minerals can be amazingly complexbut most of the time you’ll only see around 2-4 elements atone time. The size and valence state(charge) of the atoms controlthe arrangement (shape) of the cell. Different atoms have different sizes and charges Ionicradius (size) and ionic charge controlpacking o Ion – charged atom, due togain or loss of electrons o Cation- positive ion due toloss of electrons o Anion- negative ion due togain of electrons Ionicsize depends on # of electrons: anions are bigger. In ionically bonded compounds the atoms “stick”together, generally weak. Covalent bonds area lot stronger than ionically bonded compounds. They basically pass the electron back and forth within themselves. Due tothis, diamonds have a very strong, framework shape. If you see this highly complicated, framework shape it suggests that the mineral is very resistant. Bond strengths and types govern mineral properties. The type of atomicbonding governs mineral properties. o Stronger bonds = harder, higher melting points, more resistant o Weaker bonds = softer, lower melting points, less resistant. Bond strength may vary by “Direction” in a mineral. o Stronger in one direction than another ( mica is a good example.) The bonding can be simple or complex, with many different atoms They have adefinite chemical composition. o Some are complex Biotite Hornblende Minerals can have what seem like weird names The names reflecta variety of origins o Words from other languages: German – quartz (hard) How do minerals form? Solidification froma melt, from magma. It wasonce fluid, cooledoff,and the bonds began to arrange themselves in the most stable formation they could. Precipitation froma solution. o The Dead Sea – as water evaporates, the salt naturally builds up “solid solution” – you have one mineral that is made up of one chemical composition and due to heat or something(pressure), it simply rearranges into another mineral. Bio mineralization o Coral, fossil A tiny, early crystal actsas a seed for further growth. Atoms migrate to the seed and attachto the outer face. Growth moves facesoutward from the center. Unique shape reflectsthe crystal’s internal atomic order. Outward crystal growth fills the available space. Resulting crystal shape is governed by surroundings. o Open space – good crystal facesgrow o Confined space – no crystal faces. Physical Properties Color o Diagnostic for someminerals Olivine is olive green o Some minerals exhibit a broad color range. Quartz (clear, white, yellow, pink, purple, gray) Streak o Colorof powder produced by crushing amineral. o Obtained by scratching Luster o The way a mineral surfacescatters light o Two subdivisions Metallic – looks like a metal Nonmetallic Hardness o Scratching resistance of a mineral o Derives fromthe strength of atomicbonds o Hardness compared tothe Mohs scale forhardness. Specific Gravity o Represents the density of a mineral o Mineral weight over the weight of an equal water volume o Specific gravity is “heft” – how heavy it feels Fracture o The way it breaks reflectsthe atomicbonding. o Fracturing implies equal bond strength in all directions. Cleavage o Tendency to break along planes of weaker atomic bonds o Cleavage produces flat,shiny surfaces o Described by the number of planes and their angles. o Sometimes mistaken forcrystal habit. 1. Physical characteristicsreflect chemical composition 2. Minerals are arranged in mineral classes defined by their dominant anions Silicates are ¾ of Earth’s mass. Silicates and oxygens like toget together. Only about 50 minerals are abundant. Silicates are the most important minerals Silicates are the “rock-forming elements” The silicon tetrahedron is very versatile. Silicate Minerals Silicates are divided into several groups. o The groups vary by howsilica tetrahedra share oxygen Independent Tetrahedra Silica tetrahedra share no oxygens Chain silicates Silica tetrahedra link toshare two oxygens. Double Chain Silicates Silica tetrahedra alternate sharing two and three oxygens Sheet silicates Silica tetrahedra share three oxygens Create flatsheets of linked tetrahedra Framework silicates All four oxygens in eachsilica tetrahedra are shared. (Feldspars & Quartz) So what’s the idea of silicates? Which one is the most stable? Be intuitive, so sharing the most oxygens means it’s the most stable. The Si:O ratio can give you hints about the chemical and physical characteristics of a mineral. Oxides Metal cations bonded to oxygen. Sulfides Metal cations bonded to asulfide anion. Sulfates Metal cation bonded to asulfate anionic group. Many sulfates formby evaporation of sea water Salts Minerals are classified by their dominant anion. Carbonates:2 most important mineral Minerals are classified by their dominate anion.
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