Chapter 3 notes (Full)
Chapter 3 notes (Full) GEOL 1313 - 001
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This 6 page Class Notes was uploaded by Alejandra Juarez on Wednesday February 17, 2016. The Class Notes belongs to GEOL 1313 - 001 at University of Texas at El Paso taught by Musa Jad Abdel-Wahab Hussein in Winter 2016. Since its upload, it has received 257 views. For similar materials see Intro to physical geology (c) in Geology at University of Texas at El Paso.
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Date Created: 02/17/16
Chapter 3 lecture notes: Matter and Minerals Mineral: Naturally Occurring, Generally Inorganic, Solid substance, orderly crystalline structure, definite chemical composition Rock: A solid mass of minerals or mineral-like matter that occurs naturally Atoms - Smallest particles of matter that cannot be chemically split - Composed of: Protons (Charge of +1), Neutrons (charge of 0), Surrounded by electrons: Charge of -1 - Electrons exist as a cloud of negative charges surrounding the nucleus of protons and neutrons called principal shells - The outermost shells contains Valance Electrons, which interact with other atoms to form chemical bonds - Atomic Number -The number of protons in the nucleus of an atom -Determines the atom’s chemical nature Element -A group of the same kind of atoms -Approximately 90 natural elements and several synthesized in a laboratory -Organized in a periodic table so that those with similar properties line up Chemical Bonding -Formation of a compound by combining two or more elements -Transferring or sharing electrons that allows each atom to attain a full valance shell of electrons -Octet Rule: Atoms tend to gain, lose, or share, electrons until they are surrounded by eight valance electrons Ionic Bonding -Atoms gain or lose outermost (Valance) electrons to form ions (+, - charged atoms) -Ionic compounds consist of an orderly arrangement of oppositely charged ions -Ionic Bond: the attraction of oppositely charged ions to one another Ex. Table Salt Covalent Bonding -Atoms share a pair of electrons Metallic Bonding -Valence electrons are free to migrate among atoms -Accounts for the high electrical conductivity of metals Hybrid Bonding -Many chemical bonds are actually hybrids that exhibit some degree of electron sharing and some degree of electron transfer How do Minerals Deform? 1-Precipitaion of Mineral Matter - Ions dissolved in an aqueous solution reach saturation and start forming crystalline structures - A drop in temperature OR water loss through evaporation can cause ions to reach saturation 2-Crystalization of Molten Rock - Similar to water freezing - When the magma is hot, the atoms are mobile when the magma cools, the atoms slow and begin to chemically combine 3-Deposition as a result of Biological Process - Marine organisms secrete calcium carbonate ( CaCO ) 3 Physical Properties of Minerals Primary Diagnostic Properties - Determined by observation or performing a simple test - Several Physical properties are used to identify hand samples of minerals Crystal Shape or Habit 1-Mineral strength - How easily minerals break or deform under stress 2-Hardness - Resistance of a mineral to abrasion or scratching - All minerals are compared to a standard scale called the Mohs scale of hardness 3-Tenacity - Minerals resistance to breaking or deforming - Brittle minerals will shatter into small pieces - Malleable minerals are easily hammered into different shapes - Sectile minerals such as gypsum and talc, can be cut into thin shavings - Elastic minerals, such as the mica, will bend and snap back to their original shape 4-Cleavage - Tendency to break along planes of weak bonding - Produces smooth, flat surfaces - Describes by: Number of planes, Angles between adjacent planes, resulting geometric shapes 5-Fracture - Absence of cleavage when a mineral is broken: Irregular fractures, Conchoidal Fractures( Only in Hard rock),Splintery fracture, Fibrous fractures Density and specific gravity -Density is defined as mass per unit volume -Specific gravity is ratio of weight of a mineral to the weight of an equal volume of water (Most minerals have specific gravity of 2-3) Other Properties -Taste (Halite tastes like salt) -Feel (Talc feels soapy, Graphite feels greasy) -Magnetism (Can be picked up by magnet ex.loadstone) -Calcite has double refraction -Reaction to dilute hydrochloric acid (Carbonate will effervesce in acid) Optical Properties 1-Luster - Appearance of a mineral reflected light - Two basic categories: Metallic & Non metallic 2- Ability to transform light - Opaque: No lights transmitted - Translucent: Light, but no image transmitted - Transparent: Light and an image are visible through the sample 3- Color - Generally unreliable for mineral identification - Often highly variable due to impurities or slight changes in mineral chemistry 4-Streak - Color of a mineral in its powdered form - Inside streak richer than that of outside due to weathering of rock outside - Not every mineral produces a streak when rubbed against streak plate Mineral structures and compositions All minerals samples are: Crystals or Crystalline Solids (Any natural solid with orderly, repeating internal structures Mineral Structures -Steno’s law or law of constancy of constancy of interfacial angles -Regardless of crystal size, the angles between equivalent crystal faces of the same mineral are consistent Compositional variations in minerals -Ions of similar size can substitute for one another without disrupting the minerals internal framework Ex. Olivine (Mg, Fe) SiO 2 -Other minerals have trace variations in their chemical compositions Ex. Quartz (SiO 2 -The trace variations can significantly influence the mineral’s color Structural Variations in Minerals -Polymorphs: Minerals with the same composition but different crystalline structures Ex. Diamond and Graphite Transforming one polymorph into another is called a phase change Nearly 400 minerals have been named Rock-Forming minerals (Only a few dozen): Common minerals that make up most of the rocks of earth’s crust; composed mainly of the eight elements that make up most of the continental crust How Minerals Are Classified - Nearly 4000 minerals have been named - Rock-forming Minerals -Only a few dozen -common minerals that make-up most of the rocks of earth’s crust -Composed mainly of the eight elements that make up most of the continental crust - Silicate vs. Non silicate minerals -Silicate minerals are the most common type of minerals -Account for >90% of earth’s crust -Silicon and oxygen make up the basic building block of silicate minerals - Non Silicate minerals are not as common as the silicates but important economically The Silicates - All silicate minerals contain oxygen and silicon the two most abundant elements in earth’s crust - Silicate Structures -Silicon Oxygen tetrahedron: Fundamental building block -Four oxygen ions surrounding a much smaller silicon ion -Single tetrahedral are linked together to form various structures 1 Minerals with independent tetrahedral -Oxygen ions are bonded with positive ions (Such as Mg2+, Fe2+, Ca2+) Ex. Olivine, Garner Form hard dense equidimensional crystals that lack cleavage 2-Minerals with chain or sheet structures -Polymerization: The SiO4 tetrahedra can link to one another in a variety of configurations -Tetrahedra can form single chains double chains and sheet structures -Some oxygen ions are shared between tetrahedra 3-Minerals with three dimensional framework -All oxygen ions are shared between tetrahedra Ex. Quarts (Hard), the feldspars PG.104 FOR CHART Joining silicate Structures -Most silicate minerals have a net negative charge (Except for quartz) -Metal ions are required to balance the charge These positive ions bond with unshared oxygen ions in the tetrahedra Covalent silicon oxygen bonds are typically stronger that the ionic bonds of the silicate structure -Controls the cleavage and hardness of minerals Ex. Quartz has a 3 dimensional frame work is very hard and lacks cleavage Ex2. Talc has a sheet structure framework bonded with Mg ions, and is a very soft mineral Common Silicate Minerals The feldspar are the most common silicate group and make up more than 50% of earth’s crust Quartz is the 2 nd most abundant mineral in the continental crust The Light (Nonferromagnesium) Silicates: -Generally light in color -Have a specific gravity approximately 2.7 -Contain varying amounts of aluminum, potassium, calcium, and sodium -Lacking iron and magnesium The light silicate 1-Feldspar group - Most common mineral group - Forms under wide range of temperatures and pressures - Exhibit two directions of perfect cleavage at 90 degree - Two most common members: Orthoclase (Potassium feldspar), Plagioclase (Sodium and calcium feldspar) 2-Quartz - Only common silicate composed entirely of oxygen and silicon - Hard and resistant to weathering - Conchoidal fracture - Often forms hexagonal crystals - Colored by impurities (Various ions) 3-Muscovite - Common member of mica family - Excellent cleavage direction - Thin sheets are clear (Used as glass during middle ages) - Produces “glimmering” balance often seen in beach sand 4-Clay Minerals - Clay: Variety of complex minerals that have sheet structure - Makes up large percentage of soil - Chemical weathering - Kaolinite is common clay mineral used to make fine china The Dark (Ferromagnesium) Silicones - Contain iron and magnesium in their structure - Generally dark in color - Gravity between 3.2-3.6 1-Olivine group - High temperature silicates - Black to green color - Glassy luster and Conchoidal fracture - Forms small rounded crystals 2-Pyroxene group - Important components of dark colored igneous rocks - Augite is the most common mineral in the pyroxene group - Black in color - Two distinctive cleavages at nearly 90 degrees - Dominant mineral in basalt 3-Amphibole group - Humbled is the most common mineral in this group - Two perfect cleavages exhibiting angles 120 and 60 degrees 4- Biotite - Iron-rich member of the mica family - Excellent cleavage in one direction 5-Garnet - Composed of individual tetrahedra linked by metallic ions (Similar to olivine) - Glassy luster and Conchoidal fracture Important no silicate Minerals Divided into groups based on the negatively charged ion or complex ion that members have in common Make up approximately 8 percent of earth’s crust Carbonates -Composed of the carbonate ion (CO32-1) and a positive ion -Two most common carbonates are (Calcite, Dolomite) -Primary constituents in limestone and dolostone Many nobsilicate minerals have economic value -Ex. Halite (Salt) -Gypsum (Building materials) -Hematite and magnetite (Mined for iron ore) -Native elements (Gold, silver, and diamonds)
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