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Earth Materials Exam IIII (final)
ores and gems
Terms in this set (242)
anything that can be taken from the ground and make profit
an economic concentration of ore minerals
- Geologic processes make the distribution of ore deposits uneven worldwide
Groups of Ores
Metallic, Semi-Metallic, and Non-Metallic
Fertilizer and Chemical minerals
Mineral Use and Profitability
The most amount of ores taken from the Earth are used for construction and energy resources as well as salt and fertilizers
The only metal mined in large quantities
The amount of an ore in a deposit
Concentration of reserves in deposit
determined by reserves and ore grade
To remove ores
1) you must remove specific elements, compounds or minerals from an ordinary rock.
2) you must transport it
3) you must concentrate the ore
Economic Factors influencing Ore Profitability
- Extraction cost
- Market price
Low reserves, difficult location, and market variability can make a high grade ore unprofitable.
the amount an ore must be concentrated above natural crustal values to make it profitable.
- Common ores may be profitable of their concentration factor is very low.
Magmatic Ore Deposits
Igneous rocks contain accessory minerals that may contain elements of economic value.
- Cumulate ore deposits may occur in mafic and ultramafic magmas, have a crystal setting (chromite and pegmatite common)
- Fractional crystallization
an ore deposit where the ore mineral is scattered through the host rock.
Ex: diamonds are most often found this way
ores distributed in many small veins of a rock
Hydrothermal Ore Deposits
ores deposited directly from hydrothermal fluids
- may travel long distances through rocks
- deposition due to cooling, pressure, pH
- typically at mid-ocean ridges, subduction zones, or in country rock surrounding magma chamber
- Porphyries, Skarns
ore deposits in closely spaced veins due to hydrothermal activity
Volcanic Massive Sulfides
- a type of hydrothermal ore deposit commonly seen at hydrothermal vents
Sedimentary Ore Deposits
Gravity helps concentrate heavy minerals
- Deposited often by rivers, panning for gold is common.
- Other ores form from chemical precipitation like Banded Iron formations, Evaporites, and nitrates and phosphates
- weathering can also concentrate ores
Heavy minerals concentrated by gravity
- Started California Gold Rush
tropical highly leached soils rich in aluminum and sometimes nickel
Gems are values for their appearance, not their composition.
- Hardness makes certain gems valuable because of their durability
Carbonate grains that are transported as clasts and turned into limestone (Chemical Sed. Rocks)
Can be skeletal (bioclasts), non-skeletal (coated grains, ooids, peloids, or grain aggregates), or limestone clasts Iintra-, extra-)
the chemical, physical, and biological changes that effect sedimentary rocks after deposition caused by heat, pressure, and/or fluids
large scale metamorphism occuring when both temperature and pressure are high
-mountain building episodes
Contact (Thermal) Metamorphism
...Metamorphism that occurs when country rocks are subjected to high temperatures
...surrounding rock that magma intrudes
...the metamorphic zone surrounding an igneous intrusion
...change in rock composition due to the movement of fluids
...Low: 150-400 degrees
Medium: 400-600 degrees
High: greater than 600 degrees
...'mixed rock' due to partial melting
...due to increasing temperature
-if gradual and predictable it's called 'progressive'
due to decreasing temperature
common in basalts as they cool...
large crystals produced by metamorphism in a fine matrix...
...large recrystallized feldspar "eyes" in Gneiss
...long mineral grains all pointing in the same direction
minerals lining up to create a planar fabric...
a common form of metamorphic rock
- fine-grained, low-grade, dull with slatey cleavage; froms from shale and microscopic clays
common foliated metamorphic rock
- coarser grained than Slate; finer than schist
- shiny or glossy; clays have metamorphosed into small Mica grains
- wavey texture
common foliated metamorphic rock
- meduim-grained and grade; larger Mica's are being crystallized
- SCHISTOCITY=type of foliation
common form of foliated metamorphic rock
- high-grade and grain; banding of light and dark mineralscalled GNEISSIC BANDING
...mineral assemblages that indicate temperature and pressure conditions which formed in a metamorphic rock
- refers to general pressure and temperature conditions
...low temperature and high pressure
...Low temperature and low pressure
...High temperature and pressure
- also known as granulite facies
...rich in Al, Si, K and may contain Mg or Fe
- metamorphose from shales and clay rich rocks
-Quartz is essential
-muscovite and biotite present
...Quartz and Alkali Feldspar righ rocks including metamorphosed and feldspathic sandstones. Foliation is absent due to lack of micas
Mafic Rocks (metabasites)
...rich in Ca, Mg, Fe (top of bowen's)
-may form Schist and Gneiss
-Not generally Foliated
Limestones and Dolostones (Marbles)
...generally lack lineations or foliation
- if only carbonate minerals, grain size is the only significant change.
- if contains quartz or other minerals, Silicates may occur
Ultramafics and Ironstones
...Mg silicates dominate ultramafic rocks
High Pressure Metamorphic Rocks
- Blueschist Facies and Eclogites, high pressure low temperature
-Ex: Glaucophane (blue amphibole)
...came from high pressure metamorphosed mafic rocks
The Rock Cycle
1) Igneous rocks form from cooling magma
2) weathering, erosion, deposition, lithification form sedimentary rocks
3) Heat and pressure form metamorphic rocks
4) re-melting forms magma
Extrusive (Volcanic) Igneous Rocks
Extrusive igneous rocks which forms when magma is forced to the earths surface
Intrusive (Plutonic) Igneous Rocks
Intrusive Igneous rock which forms inside the earth; usually has large crystals
Aphanitic Igneous Texture
When igneous rock cools rapidly and has fine crystals
Phaneritic Igneous Texture
When igneous rock cools slowly, creating coarse grained crystals
Porphorytic Igneous Texture
Igneous cooling in a combination of slow and fast cooling that creates fine and coarse grained crystals.
Mafic Igneous Rocks
45-52% Silica (low) rich in Mg and Fe; form deep within the Earth
-Tend to be darker; form at high temperature and cannot be produced by melting crystal rocks
- Basalts and Gabbro's
Ultramafic Igneous Rocks
very high temperature igneous rocks; Serpintenite is a common alteration product.
- Peridiotite is the common term for all ultramafic rocks.
All Pyroxene means Pyroxenite
All Olivine means Dunite
Intermediate Igneous Rocks
53-65% Silica (Medium)
-medium in color
-Andesite and Diorite; Horneblende is common
Felsic Igneous Rocks
Greater than 65% Silica
- Rhyolite and granite
chemicals in magma that may concentrate as gas or vapor
-H2O and CO2 are common, Sulfur and Cl as well.
a cavity in an igneous rock formed by a trapped gas bubble
very coarse grained; may form as last incompatible elements which crystalize and form H2O-rich magma
Liquidus Igneous Crystalization
The temperature that first crystals start to form
Solidus Igneous Crystalization
The temperature that the last crystals start to form
Feldspar Igneous Silicate Group
Series: Anorthite, bytownite, labradorite, andesine, olgioclase, albite
a compositional range where no single mineral is stable under those pressure and temperature conditions
the process of a single feldspar separating into two compositions
planar layers or zones in the original grain
can be Perthite (K-spar rich with alabite)or Antiperthite (alabite-rich with K-spar)
Mica Igneous Silicate Group
Weather to Clay minerals
Pyroxene Igneous Silicate Group
Five end members:
a line connecting two end members
Amphibole Igneous Silicate Group
More chemically complicated than pyroxene group
Horneblende is most common in mafic and intermediate
Olivine Igneous Silicate Group
Mafic and Ultramafic
Foresterite and Fayalite
Corners labled SiO2, K2O/Na2O, and CaO
Used to plot silica composition of igneous rocks
Igneous Rock Occurance
Basalt is most common followed by Andesites, Rhyolites, Granitoids, Gabbro's, and alkalitic granitoids
a preserved piece of ocean floor that has been emplaced onto continental margin during a collision event
prismatic jointing perpendicular to the cooling surface of lava associated with aphanitic rocks
a vesicle filled with minerals such as Calcite, Quartz, native Copper, etc associated with aphanitic rocks.
the process that compacts sediments into sedimentary rocks through compaction and cementation
- Quartz, Hematite, and Calcite serve commonly as a cements
changing fine-grained to coarse-grained rocks
Ex: Opal-A to Opal-CT to Quartz
formed during diagenesis in place
Ex: Chert nodules
the dissolution of minerals
Silicate Sedimentary Minerals
Quartz is most resistant to weathering processes
Clay Sedimentary Minerals
Make up half the volume of sedimentary rocks
Marine Depositional Setting of Clays
- Kaolinites are common in tropics due to weathering
- Chlorites are common in poles because of LESS weathering
- Montmorillionitesare associated with Basalts on the seafloor near the East Pacific Rise.
- Illites make up the majority of temperate, mid-latitude clays (diagenic processes push things to Illite)
- Glauconites form in shallow, marine oxidized, low-sediment input settings.
Weathered volcanic ash deposits
Carbonate Sedimentary Minerals
Calcite and Dolomite are most common; essential minerals in Limestones but may occur as individual crystals or clastic fragments.
Sulfate Sedimentary Minerals
anhydrous (no water).
Halide Sedimentary Minerals
Halite and Flourite
Detrital Sedimentary Rocks
Detrital Sedimentary rocks; formed by lithification of gravel 2>mm; degree of roundness separates the two types composed of rock fragments and mineral clasts
- >30% of rock must be >2mm
Sedimentary Rock Maturity
How well sorted the fragments are
Removal of Clay
Sandstone Detrital Sedimentary Rock Classification
Chemical Sedimentary Rocks
Formed by chemical processes
The Dolomite Problem
Dolomite is rare in modern rocks, but common in ancient rock record (paleozoian and precambrian) Why?
- Three reactions:
1) Ca2+ + Mg2+ + 2CO32--->CaMg(CO3)2
2) Mg2+ + 2(CaCO3) --> CaMg(CO3)2+Ca2+
3) (CaCO3)+Mg2+ + (CO3)2- --> CaMg(CO3)2
Mixing Zone Dolomitization
Controls of Carbonate Deposition in Chem. Sed. Rocks
Increased temperature increases CaCO3 deposition
- Decreased pressure increases CaCO3 deposition
- Increased agitation of water increases CaCO3 deposition
- Organic activity helps precipitate CaCO3
non-transported limestones which are found where they form
- Micrite: generally carbonate mud
- Spar: cement crystals
Folk Classification of Sedimentary Rocks
classified limestones based on allochems and type of matrix/cement and texture
- estimate the relative abundance of carbonate grains, Micrite, and sparry Calcite based on 100%
Dunham Classification of Sedimentary Rocks
Mudstone: Mud supported, <10% large grains
Wackestone: Mud-Supported, >10% large grains
Packstone: Grain-Supported w/mud
Grainstone: Grain-supported w/o mud
Boundstone: rocks bound at time of deposition
Bindstone: later bound with microbial laminae
Framestone: originated in place as frame-built reef
Bafflestone: sediments trapped by baffling organism
Messinian Salinity Crisis
In rock record, we see there is a lot of salt deposition in the medeteranian sea. This happened when freshwater input was blocked and high temperatures caused evaporation and halite deposition
The number of anions a cation is bonded with.
- Gemoetric names given to the coordination number come from the polyhedron that is created by connecting the centers of the anions.
- Ex: Si4+ is almost always bonded with 4 Oxygens to form a silicate tetrahedron.
The spaces between the packed anions where the cation is found
Closest Packing in Two Dimensions
Closest Packing in Three Dimensions
Cubic Closest Packed
Hexagonal Closest Packed
Paulings First Rule (Radius Ratio Principle)
cation coordination number depends on the relative radii of the cation and surrounding anions.
- geometry is used to calculate limits on cation size. Very small number of cations can bond only a few anions
- as coordination number increases, space between anions increases therefore, the size of the cation that fits increases.
Pauling's Second Rule (Electrostatic Valency Principle)
strength of ionic bond is equal to the ionic charge divided by the coordination number.
Ex: Halite: 6 Na+ bonded to 6 Cl- which is octahedral coordination so the bond strength = 1/6
minerals where all bonds have the strength.
minerals that have more than two elements
Sulfates, carbonates, and nitrates.
have cations-anion bond strength that is exactly half of the charge of the anion.
Pauling's Third Rule
sharing edges or faces by coordinating polyhedra is inherently unstable.
- if polyhedra share edges or faces the cations will be too close together and repel eachother.
Pauling's Fourth Rule
Cations of high valence and small coordination number tend not to share anions with other cations.
- silicate tetrahedron
Pauling's Fifth Rule (Principle of Parsimony)
the number of different components on a crystal tends to be small.
- they normally have few types of bonds and few cation + anion sites
Isolated Tetrahedral Silicates (Nesosilicates/Orthosilicates)
- have no shared oxygens
- have minerals rich on Mg2+ and Fe2+
- Olivine and Garnet are most common
Paired Tetrahedral Silicates (sorosilicates)
- share one O between two Si.
- minerals like Epidote have paired and unpaired tetrahedra
Single Chain Silicates (Inosilicates)
- Two Oxygens are shared.
- Chains run in bands that alternate with octahedrally coordinating cations.
Ring Silicates (Cyclosilicates)
- Share two oxygens
- Tourmaline is the only common mineral that is entirely a ring silicate
Double Chain Silicates (Inosilicates)
- Share two or three oxygens
Sheet Silicates (Phyllosilicates)
three oxygens are shared
- Sheet-like tetrahedral and octahedral layers.
- Octahedral layers containing Al3+ are called Gibbsite layers
- Two ways to be layered:
1) alternating T-O layers (kaolinite or serpintine)
2) T-O-T layers (talk, clay minerals, micas, Illite, and chlorite)
Framework Silicates (Tectosilicates)
- Four oxygens are shared
- do not have enough anionic charge because of polymerization and lack small coordination sites necessary for those cations
- have low melting temperature
- Bowen's reaction series is a stability diagram
- Minerals rich in silica are more tightly bonded, therefore, more resistant to the effects of weathering.
- Quartz is most common
Simple and Coupled Substitution
Single occurs when one element replaces another with the same charge.
Coupled occurs when charge balance is maintained with two substitutions
Discovered X-rays in 1895
determined that the diffraction grating lines were to far apart to diffract X-rays; he hypothesized that the spacing of atoms in crystals could lead to X-ray diffraction.
- Received nobel prize in physics in 1914
Friedrich and Knipping
confirmed the regular crystal structure of minerals.
Bragg and Bragg
In 1913, they used X-rays to find the arrangement of atoms in Spalerite.
-Received Nobel Prize in Physics 1915
- Bragg's Law (equation)
- simplified diffraction by plane of atoms by noting that waves behave as if they were reflected from parallel planes in a crystal.
how x-rays are measured
X-rays can be related to energy because X-rays have high energy compared to other forms of electromagnetic radiation.
highest energy forms of X-rays used in manufacture industry
low energy X-rays used in medical and mineralogy that interact with the atoms in our tissue (which is dangerous)
- Energy channeled in different directions
- controlled by the X-ray wavelength and the distance between the sources of re-emitted X-rays.
- simplified diffraction by plane of atoms by noting that waves behave as if they were reflected from parallel planes in a crystal
angles between equivalent faces of crystals of the same mineral are the same.
Isomorphous Crystal Series
Minerals where the crystal structure is the same
-minerals with identical atomic distributions, even if they have the same compositions
How the pattern of unit cells is described
All crystals basic building blocks
Symmetry with respect to a point(different from point groups)
-Repeats something a limited number of times and is localized around a central point.
repeats something in infinite number of times to fill a space.
- Ex: translation (a type of space symmetry)
Five 2D Unit Cells or Plane Lattices
design that repeats its self
A type of space symmetry
- a repeating motif
- the distance between translation is the difference between lattice points
Primitive and Doubly Primitive Unit Cells
Primitive: unit cells that contain one motif
Doubly: Two motifs
Centered Unit Cells
Second Law of Crystallography
If a motif has a certain symmetry then the lattice must have at least that much symmetry.
Ex: if a motif has 4-fold symmetry the lattice must also have at least 4-fold symmetry
Third Law of Crystallography
The symmetries of unit cells are the same as the point groups of greatest symmetry in each of the crystal systems.
Fourth Law of Crystallography
If a crystal has a certain symmetry, the unit cell must have at least that much symmetry. If a crystal has a certain symmetry, the unit call AND atomic structure must have at least that much symmetry.
Cubic Crystal System
-a=b=c @ 90
-Has the highest number of symetry: four 3-fold axes
-Usually isotrophic (same properties in all directions)
- Ex: Garnite, Halite, and pyrite
Tetragonal Crystal System
a=b does not = c @90
- one 4-fold axis
- Optically uniaxial parallel to 4-fold
Hexagonal Crystal System
- a=b does not = c @ 60
- has one 3-fold or 6-fold axis of symmetry
- Optically uniaxial parallel to 3 or 6 fold axes.
- Often grow as prisms with three or six sides
- Ex: quartz and corundum
Monoclinic Crystal System
two equal, one not equal 2 @ 90, 1 not @90
- Single, 2-fold axes or mirror planes
- "shoeboxes" with one corner is smooshed (not at 90 degrees) (pink eraser)
- Optically biaxial
- Ex: diopside and gypsum, orthoclase
Triclinic Crystal System
- none equal, none at 90
- No symmetry greater than one-fold
- Optically biaxial
- Ex: alabite, amazonite
Orthorhombic Crystal System
- a does not = b does not = c @ 90
- Two perpendicular mirror planes
- three perpendicular 2-fold axes (shoebox)
- Optically biaxial
- Ex: sulfur and topaz
14 distinctly different space lattices created from the unit cells of the six crystal systems
have reflection symmetry; a plane existing within the shape that reflects a mirror image
-Reflection is the operation; the mirror plane is the operator.
-A crystal cannot have more than nine mirror planes
-Cubes have nine mirror planes
-Symmetry with respect to a line
-an "imaginary" line through the center of the shape, extending perpindicular to paper. How many times does the shape repeat its self during a complete 360
Isymmetry with respect to a point or inversion center (symbolized by i)
-"center of symmetry"
Having few symmetry elements
Having lots of symmetry elements
Plotting on a Stereo Diagram
1) center crystal into a sphere
2) perpindicular lines are extended to connect the sphere to the crystal
3) points are then projected onto the equatorial plane of the sphere to create a two dimensional drawing
a combination of rotation and inversion
combinations of symmetry elements
a set of identical faces related by symmetry
Rock forming process
white light which contains wavelengths of all the primary colors in nearly equal intensity
...only one wavelength of light
...whether a wave is moving up or down at a given time.
...waves interacting in phase
...wavelengths interacting out of phase
Plane Polarized Light
...polarized vibrations in a single plane
Cross Polarized Light
...samples viewed with the upper polarizer as well as the lower polarizer
Parts of a Petrographic Scope
...change in color as the stages is rotated; colors may be more intense than they are in plane polarized light
...intense cross polarized colors
- can be used to identify minerals
...-a light waves velocity through a crystal
- function of chemical composition, structure, and bond type
...Different properties in different directions
- most minerals
- do not appear extinct under cross polarized light, go extinct every 90
...minerals have some optical properties in all directions
- appear extinct in XP light when stage is rotated
...has one optic axes
...have two optic axes
relates the angle of the incoming beam, the difference in velocity, and the refractive index of each medium
describes the visible contrast between a mineral and a liquid of known refractive index
High relief grains stand out dramatically
Low relief grains are barely visible
...used to determine if a mineral has a high or low refractive index than the liquid medium they are in
the splitting of a light beam into two perpendicularly polarized rays
O-Ray and E-Ray
...polarized light passing through an anisotrophic mineral and split into two polarized rays traveling in two different paths with different velocities
- always perpindicular to each other
Slow and Fast Ray
...in anisotrophic minerals they are the two rays traveling at different velocities, their refractive indices must be different
...the difference between the slow and fast ray
...the distance the fast ray is ahead of the slow ray when it leaves the crystal
...the plane containing the X, Z and two optic axes
...the external shape of the internal structure of a mineral
Equant, blocky, and acicular
...no crystal faces
...fully developed crystal faces
...elements that have different mass due to number of neutrons
O16, O17, O18
a high temperature mineral related to quartz
...the minerals ability to transmit light that can be classified as...
Transparent, Translucent, or opaque
...mineral gets its color from components
Thin Sections Plagioclase
...Has zebra-stripping or "Plagioclase twinning" which is dark to light-grey in color.
Thin Sections Orthoclase
...Doesn't quite have twinning that Plagioclase exhibits, appears more "dirty" than quartz because it weathers more easily.
Thin Sections Quartz
...Has low relief and has large phenocrysts with rounded edges which are clear in PP light and exhibits undulating extinction when the base is rotated.
Thin Sections Muscovite
...Clear in PP, but has high interference colors in XP
Thin Sections Biotite
...Color is tan or brown in PP light, exhibits "pebbly" texture or birds-eye extinction.
-"sandy" in XP light; appears in flake shape
Thin Sections Olivine
...has high relief and high interference colors with a tendency of being a dark blue under XP light
Thin Sections Horneblende
...appears more green than Biotite
-has smooth surface
-sometimes can see cleavage
-exhibits rouded, patchy, diamond pattern
Thin Section Augite
...has dusty green-grey color in PP light; appears more blocky than Horneblende
Thin Section K-spar
Has characteristic tartan (checkerboard) twinning
Thin Section Sanidine
exhibits 1/2 and 1/2 twinning with greys
Thin Section Epidote
is clear in PP light, exhibits high interference colors in XP light
Silicate Mineral Class
Single, double chain, sheet, framework, ring,
Oxide Mineral Class
make up some of the most important ores
Hydroxide Mineral Class
Orthorhombic; contain hydrozides
Limonite and Goethite
Sulfide Mineral Class
Polymorphs of pyrite (Marcasite)
Sulfate Mineral Class
Gypsum (hydrous or anhydrous) Anhydrite
Phosphate Mineral Class
Carbonate Mineral Class
Calcite, Aragonite, Dolomite
Halide Mineral Class
Halite and Flourite
Graphite, Sulfur, Gold, Copper, Iron, Platinum, Silver
the parts of sedimentary rock that are resistant to chemical weathering
the dissolved material in chemical weathering
the process of dissolution and alteration to make new materials in chemical weathering
crystalline solid with narrowly defined chemical composition and characteristic physical properties
The appearance of light on the surface of a mineral
metallic, non-metallic, or sub-metallic
color producing elements in a mineral
mineral gets its color from trace elements
Play of Colors
resistance to breaking or deformation
-controlled by the type of bonds
fully developed crystal faces
in between euhedral and anhedral
substances that have random atomic structure
Having the same properties in all directions
having different properties in different directions
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