Geology Chapter 3: Earth Materials – Minerals and Rocks – Flashcards
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mineralogy
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branch of geology that studies the composition, structure, appearance, stability, occurrence, and associations of minerals
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mineral
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a naturally occurring solid crystalline substance, usually inorganic, with a specific chemical composition: minerals are homogenous - they cannot be divided mechanically into smaller components
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what does 'minerals are homogenous mean'?
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they cannot be divided mechanically into smaller components
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what does 'minerals are naturally occurring mean'?
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to qualify as a mineral, a substance must be found in nature (not produced synthetically)
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what does 'minerals are a solid crystalline substance mean'?
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crystalline refers to the fact that tiny particles of matter (or atoms) that compose the mineral are arranged in an orderly, repeating, three-dimensional array
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amorphous
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= glassy = without form - these are substances that do not have an orderly crystalline arrangement and are not deemed minerals
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what is organic matter?
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it is matter composed of organic carbon which is found in all organisms living or dead
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What is the smallest unit of an element that retains the physical and chemical properties of that element?
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An atom
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Structure of an atom
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Consists of a dense nucleus which contains virtually all of its mass in protons and neutrons. The nucleus is surrounded by a cloud of moving particles called electrons
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Charge of a proton
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+1
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Charge of a neutron
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electrically neutral
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Charge of an electron
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-1
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What do atoms of the same chemical element have in common?
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Always have the same number of protons but may have different numbers of neutrons. An atom is electrically neutral because the number of protons is balanced by the number of electrons surrounding it
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Atomic number
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number of protons in the nucleus of an atom. Periodic table is organized by atomic number
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Atomic mass
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sum of an atom's masses of protons and neutrons. Electrons are not included since their mass is virtually negligent
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Isotopes
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Atoms of the same element with different numbers of neutrons
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Why are average atomic masses never whole numbers?
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Chemical elements in nature exists as mixture of isotopes meaning their atomic mass is an average of various numbers and closest to the isotope with the highest relative abundance
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Chemical reaction
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Interactions of the atoms of two or more chemical elements in certain fixed proportions --> produces chemical compounds which may properties entirely different from those of its constituent elements
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Electron sharing
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mechanism by which a covalent bond is formed between the elements in a chemical reaction
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Electron transfer
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mechanism by which an ionic bond is formed between the elements in a chemical reaction
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How are chemical compounds produced?
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Through chemical reactions that result in either electron sharing between the reacting atoms or by electron transfer between the reacting atoms
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Ion
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Atom or group of atoms that has an electrical charge, either positive or negative, because of the loss or gain of one or more electrons
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Cation
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positively charged ion
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Anion
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negatively charged ion
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Chemical bond
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electrostatic attraction between negatively charged electrons and positively charged protons which holds the compound together. May be weak or strong but strong bonds keep a substance from decomposing into its elements/other compounds
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Ionic bonds
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Form by electrostatic attraction between ions of opposite charge - 90% of all minerals are ionic bounds
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covalent bonds
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sharing of electrons which occurs when elements do not readily gain/lose electrons
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Metallic bonds
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when atoms of metallic elements bond they have strong tendencies to lose their electrons. The atoms thus pack together as cations and the freely mobile electrons are shared/dispersed among the cations
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Crystallization
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atoms of a gas or liquid come together in the proper chemical proportions and in the proper arrangement to form a solid substance --> how minerals are formed
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Crystals
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orderly three-dimensional arrays of atoms in which the basic arrangement is repeated in al directions
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Crystal faces
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= boundaries of crystals which are natural flat (planar) surfaces. These are the external expression of the mineral's internal atomic structure
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Grains
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crystalline particles that are formed when crystals do not have space to grow or the crystallization occurs rapidly, resulting in the crystals growing over one another and coalescing to become a solid mass of these - usually do not show crystal faces
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How does crystallization occur?
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when the temperature of a liquid is lowered below its freezing point (for magma, below its melting point), or when liquids evaporate from a solution
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Polymorphs
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minerals with alternative structures formed from the same chemical element or compound
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How are minerals classified?
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usually classified by their anions (i.e. SiO4^4- is classified as a silicate because of its silicate ion)
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What are the five most common classes of rock-forming minerals?
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Silicates - must abundant class of minerals (= O + Si) Carbonates - composed of carbon and oxygen Oxides - compounds of oxygen anion and metallic cations Sulfides - compounds of the sulfide anion and metallic cations Sulfates - compounds of the sulfate anion and metallic cations
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Name the physical properties of minerals
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Hardness, cleavage, fracture, luster, color, density, crystal habit
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Hardness
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= a measure of the ease with which the surface of a mineral can be scratched. Mohs scale of hardness is used as a measure. The hardness of a mineral depends on the strength of its chemical bonds - greater the strength, the harder the mineral
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Mohs scale of hardness
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Scale based on the ability of one mineral to scratch another. 1 = talc --> softest 2.5 = fingernail 3.5 = copper coin 7 = quartz 10 = diamond --> hardest
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Are covalent or ionic bonds stronger?
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Covalent bonds are stronger --> result in harder rocks
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What other factors other than bond strength affect a mineral's hardness?
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Among minerals with similar crystal structures, size, charge, and packing affects their hardness. Smaller the atoms = smaller distance between them - greater electrostatic attraction --> stronger bond Larger the charge, greater the attraction --> stronger bond Closer the packing --> stronger the bond
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Cleavage
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= tendency of a crystal to split along planar surfaces and describes the geometric pattern produced by breakage. Cleavage varies inversely with bond strength - strong bonds have poor cleavage, weak bonds have strong cleavage. Characterized by the number of planes and pattern of cleavage
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Do strong bonds or weak bonds have better cleavage? Covalent vs. ionic?
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Weak bonds = better cleavage Covalent bonds = poor/no cleavage Ionic bonds = good cleavage
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What is cleavage characterized by?
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Number of planes & pattern of cleavage
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How is a mineral's cleavage assessed?
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Either as perfect, excellent, good, fair, poor, or none (i.e. muscovite's cleavage = perfect)
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Minerals with different types of cleavage
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1 plane: muscovite 2 planes: feldspar, hornblende (2 cleavages at 120 degrees) 3 planes: halite, galena (3 cleavages at 90 degrees) 4 planes: calcite
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Fracture
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= tendency of a crystal to break along irregular surfaces other than cleavage planes - related to how bond strengths are distributed in directions that cut across cleavage planes
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How are fractures characterized?
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Conchoidal (= smooth, curved surfaces like broken glass), fibrous/splintery (like split wood)
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Luster
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= the way the surface of a mineral reflects light - determined by the kinds of atoms present and their bonding (affects the way light passes through/is reflected)
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What kind of luster do ionic bonds tend to have? Covalent bonds?
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ionically bonded crystals tend to have a glassy/vitreous luster Covalently bonded minerals are more variable
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Types of mineral lusters
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metallic = strong reflections produced by opaque substances vitreous = bright, as in glass resinous = characteristic of resins, such as amber greasy = appearance of being coated with oily surface Pearly = whitish iridescence of such materials as pearl Silky = sheen of fibrous materials such as silk adamantine = brilliant luster of diamond
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Color
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= imparted by light, either transmitted through or reflected by crystals. Color may not be reliable as some minerals have a range of colors - use streak in this case. color depends on the presence of certain ions that absorb portions of the light spectrum
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Streak
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= color of the fine deposit of mineral power left on an abrasive surface such as a tile of unglazed porcelain (= streak plate)
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Trace elements
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= elements that make up less than -0.1% of a mineral
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Density
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= depends on the atomic mass of a mineral's atoms/ions and how closely they are packed in its crystal structure. Often measured by specific gravity which is the weight of a mineral divided but the weight of an equal volume of pure water at 4 degrees Celsius
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Density/specific gravity of well-known minerals
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Quartz = 2.65 Calcite = 2.7 Galena = 7.2-7.6 Hematite = 5.2
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Crystal habit
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= shape in which individual crystals or aggregates of crystals grow (i.e. needles, platy, fibrous, globular). This depends on the planes of a mineral's crystal structure and the typical speed/direction of crystal growth
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Rock
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= naturally occurring solid aggregate of minerals or in some cases non mineral solid matter. They vary in color, sizes of crystals, and in the kinds of mineral that compose them. Rocks are identified partly by their mineralogy and partly by their texture
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Texture
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describes the sizes and shapes of a rock's mineral crystals or grains (i.e coarse vs. fine-grained) and the way they are put together
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Igneous rocks
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= all rocs formed by the solidification of molten rock (i.e. basalt/granite)
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sedimentary rocks
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= all rocks formed as the burial products of layers of sediments (i.e. sand, mud, calcium carbonate shells ,etc.) - can be laid down by land or sea
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metamorphic rocks
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= formed by the transformation of preexisting solid rocks under the influence of high temperatures and pressures
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What is the source material and the rock forming process of igneous rocks?
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- Melting of rocks in hot, deep crust and upper mantle - crystallization = solidification of magma/lava
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What is the source material and the rock forming process of sedimentary rocks?
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- weathering and erosion of rocks exposed at surface - deposition, burial, lithification
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What is the source material and the rock forming process of metamorphic rocks?
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- rocks under high temperatures and pressures in deep crust and upper mantle - recrystallization of new minerals in solid state
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What is the difference between how coarse-grained and fine-grained igneous rock is produced?
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coarse-grained: magma cools below melting point in Earth's interior allowing some crystals to grow larger before the whole mass crystallizes fine-grained: magma erupts from volcano on Earth's surface and cools so rapidly that crystals do not have time to grow
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Intrusive igneous rocks
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crystallize when magma intrudes into unmelted rock masses deep in Earth's crust --> produces coarse-grained rocks characterized by large interlocking crystals (i.e. granite)
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Extrusive igneous rocks
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form from magmas that erupt at the Earth's surface as lava and cool rapidly --> produces fine-grained rocks characterized by glassy texture (i.e. basalt)
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Common minerals of igneous rocks
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Most minerals are silicates such as quartz, feldspars, micas, pyroxenes, amphiboles, and olivines
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Sediments
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= layers of loose particles found at the Earth's surface (ie. sand/shells of organisms) - particles originate in the processes of weathering/erosion
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Weathering
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= all chemical/physical process that break up and decay rocks into fragments and dissolved substances of various sizes
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Erosion
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set of processes that loosen soil and rock and move them downhill or downstream to the spot where they are deposited as layers of sediment
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What are the two ways sediments can be deposited?
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Siliciclastic sediments - made up of physically deposited particles (i.e. grains of quartz and feldspar derived from weathered granite) - laid down by running water wind and ice Chemical & biological sediments - new chemical substances formed by precipitation when weathering dissolves some of a rock's components, carries them to the ocean and it precipitates from evaporating seawater or organisms
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Lithification
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= process that converts sediments into solid rock
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What are the two ways lithification can work?
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compaction = particles squeezed together by weight of overlying sediments into mass denser than original cementation = minerals precipitate around deposited particles and bind them together
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Bedding
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= formation of parallel layers of sediment as particles are deposited (characteristic of sedimentary rocks)
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What are the common minerals of sedimentary rocks?
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Most common in siliciclastic sediments are silicates (quartz, feldspar, clay minerals) Most common in chemical/biological sediments = carbonates = main constituent of limestone
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Regional metamorphism
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= occurs where high pressures and temperatures extend over large regions, as happens when plates collide --> accompanies plate collisions that result in mountain building and the folding and breaking of sedimentary layers that were once horizontal --> usually show characteristic foliation (wavy or flat planes)
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Contact metamorphism
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= where high temperatures are restricted to smaller areas such as in the rocks near/in contact with magmatic intrusion
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Common minerals of metamorphic rocks
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Silicates are the most abundant (quartz, feldspars, micas, pyroxenes, amphiboles)
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Rock cycle
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= set of geological processes that convert rocks of each of the three major types into the other two types. It is a result of the interactions of the plate tectonic and climate system
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concentration factor of an element in a mineral deposit
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= ratio of the element's abundance in the deposit to its average abundance in the crust
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ores
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= rich deposits of minerals from which valuable metals can be recovered profitably --> result of hydrothermal solutions
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hydrothermal solutions
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= hot water solutions that are formed around bodies of molten rock - these allow for the formation of large ore deposits when circulating water comes in contact with the magmatic intrusion, reacts with it, and carriers off significant quantities of elements and ions released by the reaction
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veins
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= tabular/sheetlike deposits of precipitated minerals that form in the fractures of rocks when hydrothermal solutions move through them
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disseminated deposits
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= deposits of ore minerals that are scattered through volumes of rock much larger than veins --> also result of hydrothermal solutions
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What are the major rock forming minerals?
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Light colored (felsic) - quartz - feldspar (alkali (orthoclase), plagioclase) - mica (muscovite) Dark colored (mafic) - pyroxene (augite) - amphibole (hornblende) - olivine - mica (biotite) Calcite (CaCO3)
