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222 Cards in this Set
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Mineral |
naturally occurring, crystalline solid with an orderly internal atomic arrangement. It has specific chemical composition and is formed through geological processes |
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Mineraloids |
mineral-like substances that don't strictly meet the definition ex.) opal-has water in it obsedian-glass |
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Rock |
an aggregate of minerals and need not have a specific composition |
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The majority of crustal rocks are composed of: |
silicate minerals |
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silicate minerals: |
minerals with Si in their formula |
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coordination # |
how many anions are around the cation |
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motif |
a set of atoms arranged in a particular way |
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lattice |
an array of points repeating periodically in 3D |
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The unit cell |
a tiny box containing one or more motifs -the volume outlined by the lattice nodes |
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the unit cells staked in 3D space describes the: |
bull arrangement of atoms in the crystal |
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6 different crystal systems: |
cubic tetragonal orthorhombic hexagonal monoclinic triclinic |
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cubic: |
a=b=c beta=alpha=gamma |
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tetragonal: |
a=b not equal to c alpha=beta=gamma |
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orthorhombic
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a not equal to b not equal to c alpha=beta=gamma=90 |
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monoclinic |
a not equal to b not equal to c alpha=gamma=90 not equal to beta |
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triclinic |
not lengths the same no angles the same |
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crystal form |
-cubic -hexagonal -rectangular etc. |
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crystal habit |
typical appearance of mineral -blocky, acicular, tabular/platy, bladed, prismatic, foliated |
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hardness |
hardness is resistance to scratching |
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mineral hardness is related to |
the bond strength within the mineral |
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cleavage |
minerals either cleave along // planes or they fracture irregularly (no cleavage) |
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cleavage vs crystal faces |
-crystal faces may show a variety of growth features (twinning, striations etc.)
-cleavage surfaces are indicated by // fractures |
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lustre |
-lustre represents the qualitative expression of light reflection from a mineral ex. metallic, glassy (vitreous), silky, dull, earthy etc |
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colour |
the least dependable of the properties used for mineral id |
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streak |
the colour of the powder of a mineral when scratched on a porcelain plate |
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twinning |
a growth phenomenon defined as the symmetrical inter growth of 2 or more crystals of the same substance |
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Silicate classes: |
1. orthosilicates (nesosilicates) 2. disilicates (sorosilicates) 3. ring silicates (cyclosilicates) 4. chain silicates (inosilicates) 5. sheet silicates (phyllosilicates) 6. framework silicates (tectosilicates) |
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orthosilicates |
nesosilicates -has the least degree of polymerization -NO oxygen anions are shared between adjacent tetrahedra |
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formula of orthosilicates: |
(SiO4)-4 |
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examples of orthosilicates |
olivine zircon garnet aluminum silicates staurolite chloritoid topaz titanite |
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Net charge is balanced by: |
bonding with other cations such as Mg+2, Fe+2, Al+3 |
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Disilicates |
Sorosilicates -share a single O-2 between 2 silicon tetrahedra |
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Examples of dislocates |
-epidote group -lawsonite -pumpellyite |
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Ring silicates |
(cyclosilicates) -the tetrahedra share 2 O-2 each and form rings, usually 6-sided |
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Examples of cyclosilicates |
tourmaline beryl (emerald) cordierite |
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formula of cyclosilicates |
(Si6O18)-12 |
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formula for sorosilicates |
(Si2O7)-6 |
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Single chains |
Inosilicates 2 O-2 per tetrahedra are shared with neighbouring tetrahedra |
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formula of inosilicates |
(SiO3)-2 |
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Pyroxenes are constructed of: |
single chains of tetrahedra that extend parallel to the c-axis |
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TOT chains: |
tetrahedral-octahedral-tetrahedral -form "i-beam" |
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pyroxene cleavage angles: |
87 - 93 degrees |
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TOT structures in pyroxene: |
strong, cleavage cuts around them |
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Double Chains |
some tetrahedra share 2 O-2 and others share 3 O-2 |
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Amphiboles are constructed of: |
double chains of tetrahedra that extend parallel to the c-axis and are stacked in alternating fashion |
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cleavage angles of amphiboles" |
56-124 degrees |
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Sheet Silicates |
Phyllosilicates -share 3 O-2 per tetrahedra to form continuous sheets |
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formula of phyllosilicates |
(Si4O10)-4 |
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formula of single chain silicates: |
(SiO3)-2 |
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formula of double chain silicates |
(Si4O11)-6 |
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In sheet silicates there are lots of substitutions of: |
Al+3 for Si+4 |
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all sheet silicate are: |
hydrous, meaning that hydrogen is in the structure (usually OH-) |
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T sheets are always: |
joined with an O-sheet to make TO or TOT layers |
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Divalent cations: |
need 3 cations in the formula to balance the charge example: Talc -3 Mg |
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Trivalent cations: |
need 2 cations in the formula to balance the change example: pyrophylitte - 2 Al |
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When the cations are divalent. we call the O sheet a: |
trioctahedral sheet -subscript 3 |
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When the cations are trivalent, we call the O sheet a |
dioctrahedral sheet -subscript 2 |
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What is the interlayer cation in micas? |
K+ |
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Cleavages in the micas: |
-the interlayer K+ are ionically bonded to the TOT layers, which makes micas a bit harder then talc, serpentine, koalinite, pyrophyllite |
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Where do micas break? |
between the interlayer |
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Framework silicates |
tectosilicates -all 4 O-2 on each tetrahedra are shared with adjacent tetrahedra to form a 3D framework |
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formula of complex anion: |
(SiO2)^0 -net zero charge |
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what is the ratio of Si(Al) in tetrahedra coordination: O in framework silicates |
1:2 ratio |
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framework silicates are the most: |
highly polymerized silicate group |
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The open crystal structure of framework silicates means that they can: |
easily accommodate BIG cations like Ca+2, Na+, K+ into their structures -this means they have higher coordination numbers like 8,9 or 12 |
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What is the consequence of framework silicates accommodating big cations into their structure: |
-the specific gravity of the framework silicates is much lower then many other minerals quartz: 2.65 olivine: 3.27- close packed crystal structure |
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Framework silicates tend not to be: |
stable at high pressures and are generally restricted to the earths crust |
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groups of framework silicates: |
silica group feldspar group feldspathoid group zeolite group |
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silica group framework silicate:
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-quartz |
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feldspar framework silicate group: |
-coupled substitution of 3 end members K-feldspar: KAlSi3O8 Albite: NaAlSi3O8 Anorthite: CaAl2Si2O8 -adding the cation balances the total charge |
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feldspathoid framework silicate group: |
-Have less Si relative to the amount of Na and K -fairly uncommon |
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Zeolite framework silicate group: |
-hydrated framework work silicates |
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Idealized feldspar structure: |
-K-feldspar has 4 tetrahedral sites called T1 & T2
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K-Feldspars: |
KAlSi3O8- one Al+3 substitutes for one Si+4 |
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Types of K-spars: |
-Sanidine -Orthoclase -Microcline |
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Sanidine: |
-high T -Al can substitute for any Si -completely disordered |
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Orthoclase: |
-intermediate T -intermediate number of sites with al |
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Microcline: |
-low T -Al restricted to one site -completely ordered Si fills the other 3 sites |
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Degree of order depends on: |
temperature |
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high T favours : |
disorder |
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Low T favours |
order |
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plagioclase twinning: |
albite twins |
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plagioclase twinning: |
carlsbad twinning |
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Perthitic Texture |
-seen in alkali feldspars -Na+ & K+ separate into different domains during cooling -needs slow cooling, plutonic rocks |
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Iridescence |
-exsolution seen in plagioclase feldspars -certain surfaces change colour as the angle or view changes |
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Types of pyroxene: |
-Clinopyroxene -Orthopyroxene |
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Types of Amphibole: |
Orthorhombic series: anthophyllite Monoclinic series: temolite, actinolite, cummingtonite, grunerite, hornblende |
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n= |
refractive index |
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The amount of refraction that occurs depends on: |
the difference in R.I of the 2 media or materials |
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The amount of refraction can be described by: |
shells law n1sin(0)1=n2sin(0)2 |
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RI equals: |
n=speed of light in vacuum/sped of light in the material |
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speed of light in a vacuum: |
2.99x10^8 m/s |
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The higher the RI: |
The MORE light is slowed down as it passes through the crystals |
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What is becke line? |
Becke line is the band or rim of light visible along a grain/crystal boundary |
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Why do becke lines appear?
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mineral in thin section tends to be thicker in the centre and thinner towards the edge, thus they act as lenses |
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The direction of movement of the becke line is determined by: |
lowering the stage with the becke line always moving into the material with the higher RI (in ppl) |
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In an optical microscope, the polarizer at the bottom: |
polarizes the light |
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Isotropic minerals: |
-has the same properties in all directions -this means light passes throughout them in the same way with the same velocity -black in XPL -common minerals: garnet and spinal |
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Anisotropic minerals: |
-the velocity of light varies depending on direction through the mineral -most minerals are anisotropic -light traveling through splits into 2 rays that travel with different velocities -fast and slow ray |
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How does electromagnetic theory explain why light velocity varies with direction when it travels through an anisotropic mineral? |
1.) strength of chemical bonds and atom density are different in different directions for anisotropic 2.) a light ray will pass through a different electronic arrangement depending on the direction it takes through a mineral |
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Retardation: |
In the time it takes the slow ray to pass through the mineral the fast ray will have traveled through the mineral PLUS an additional distance. additional distance: retardation |
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Birefringence: |
the difference in the index of refraction of the slow ray (ns) and the fast ray (nf) |
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equation of retardation: |
retardation = d (ns-nf) retardation = thickness of mineral (birefringence) |
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Feldspar and quartz interference colours: |
1st order ex. grey |
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biotite and muscovite interference colours: |
3rd order |
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polarizer: |
lets light pass through with a E-W vibration direction |
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analyser: |
lets light pass through with a N-S vibration direction |
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When does extinction occur? |
when the polars are crossed when you rotate the stage |
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opaque minrals: |
do not transmit light in thin sections -appear black in PPL and XPL -graphites, oxides and sulfides |
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Pleochroism |
property of minerals in PPL -ability of a mineral to absorb different wavelengths of transmitted light depending upon its crystallographic orientation |
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igneous means: |
born of fire |
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how do igneous rocks form? |
by crystallization from a magma (+700C) -as the magma comes up towards the surface, it gradually cools, and crystals start to form |
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3 types of plate boundaries: |
-transform -divergent -convergent |
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transform boundaries |
2 plates sliding by one another -crust neither created nor destroyed -not a major source of igneous rocks |
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divergent boundaries |
-2 plates moving away from each other -mid ocean ridges -crust is created -largest source of igneous rocks |
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convergent boundaries |
2 plates colliding with one another -crust is recycled -subduction zones -continent-continent collision; lots of plutonic igneous rocks |
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Why does the continental crust rift over the EARZ? |
-2 large mantle plumes under the EAR, pushing the continent apart |
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Examples of rift valleys: |
Red Sea Gulf of California |
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Ocean-Ocean convergence: |
-cooler oceanic plate subducts underneath island arcs (also oceanic crust), creates a deep sea trench |
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Partial melting |
-generates magama -subducting plate dehydrates, releases water into mantle, induces melting -magmas rise and fuel island arc volcanoes on landward side of the deep sea trench |
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Ocean-Continent Convergence |
-continental lithosphere more buoyant; ocean plate sub ducts |
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Obduction: |
occasionally oceanic crust thrusts over top of continental crusts, creates ophiolite |
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example of ocean continent convergence: |
-coast mountains in BC: juan de fuca plate below N.A plate -nazca and south american plate |
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Continent- continent convergence |
-leads to extremely high topography at early stages example: Himalaya |
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"doubling" of continental crust causes: |
isostatic forces to make very thick crust and high mountain ranges |
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What is common in continent-continent convergence zones: |
-deep crustal melting, forms felsic plutonic rocks
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J. Tuzo Wilson theory: |
1963 -Volcanoes "punched out" of pacific ocean as crust passes over "hot spot" |
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hot spot: |
area of volcanic activity produced by a plume of magma rising in the mantle -fixed in place, plates move over top |
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As volcanic islands approach the Aleutian trench: |
the increase in age |
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Intrusive igneous rocks are also called: |
plutonic rocks |
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Intrusive rocks form: |
when magmas intrude into unmelted rock masses deep in the Earths crust -cool slowly |
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Intrusive rock texture: |
Phaneritic large, interlocking crystals due to slow cooling |
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Example of intrusive rock: |
granite |
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Extrusive igneous rocks are also called: |
volcanic rocks |
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how do extrusive rocks form |
form from magma which erupts at the surface of the earth through volcanoes -cool rapidly |
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extrusive texture: |
Aphanitic -very fine grained or glassy due to rapid cooling |
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example of extrusive rock: |
basalt |
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what are rock textures that are texturally intermediate: |
-hypabyssal -medium-grained |
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Anorthosite: |
<10% mafic minerals |
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Diorite: |
>10% mafic minerals -black and grey rock |
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Gabbro |
>10% mafic minerals -medium-dark grey, dark rock |
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TAS classification: |
Total Alkali Silica classification -when the volcanic rock is to fine grained to identify the minerals 1. must be volcanic 2. must be fine grained 3. must be unaltered 4. must have chemical analysis |
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Lava or Flows |
magma flows onto the surface as a liquid and solidifies -basalt, andesite, rhyolite |
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Pyroclastic rocks and tephra |
-a clastic rock composed solely or primarily of volcanic materials (pyroclasts) -explosive products of volcano -clastic: lots of things cemented together |
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Types of pyroclasts: |
-bombs -blocks -lapilli -ash grains |
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bombs |
>64 mm shape indicates they were wholly or partly molten during the formation and transport |
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blocks: |
>64mm -angular/subangular shape indicates that they were solid during transport,formation |
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lapilli |
2mm-64mm -pyroclasts of any shape, spherical, aggregates of ash making a ball shape |
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Ash grains |
coarse ash grains: 2mm-1/16mm fine ash: dust |
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unconsolidated deposits: |
tephra |
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consolidated deposits: |
pyroclastic rocks |
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The main factor that determines the texture of an igneous rock: |
cooling rate dT/dt |
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Crystallinity scale: |
100% crystals: holocrystalline intermediate: hypocrystalline/hypohaline 100% glass: holohyaline |
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Phaneritic crystal size: |
fine grained: <1mm medium: 1-5 mm coarse: 5-20 mm very coarse: >20mm |
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Phaneritic rock textures: |
-porphoritic -granular -hypidiomorphic granular -pegmatitic -graphic -myrmekitic texture |
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Porphoritic texture: |
different grain sizes |
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equigranular texture: |
same sized gains |
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hypidiomorphic granular: |
range of euhedral, subhedral, anhedral crystals |
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pegatitic texture: |
-very coarse, involving feldspars and quartz >20mm crystal size -often contain rare earth minerals (aquamarine, tourmaline, topaz, fluorite, apatite) |
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graphic texture: |
inter growths of quartz and k-felds -resembles cuneiform writing -observed in pegmatites |
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myrmekitic texture: |
inter growth of quartz and play, shows small wormlike bodies of quartz enclosed in play -found in granites~ |
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Aphanitic crystal size |
-Cannot be seen with unaided eye, very small -extrusive rocks! cooled rapidly |
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glassy crystal size indicates |
that the molten material crystallized very rapidly and there was no time for elements to arrange themselves into solid crystalline compounds |
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Is obsedian mafic or felsic? |
obsedian is extremely felsic depict dark colour -consists of 70%+ of SiO2 |
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Aphanitic crystal textures: |
-spherulitic -fragmental -porphyritic -glomeroporphyritic -poikilitic texture -rapaki granite -corona texture |
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spherulitic texture: |
-commonly found in glassy rhyolites -intergrowths of radiating quartz and feldspar replace bass as a result of devitrification |
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crystal size fragmental: |
-fragmental rocks consist of pyroclastic material ejected as lava from a volcano which falls down as partly consolidated rocks -igneous on way up, sedimentary on the way down |
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Porphyritic texture |
-forms with 2 stages of cooling, bigger crystals grow first possibly still in magma chamber, erupts, smaller gains cool quickly above ground |
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Glomeroporphyritic texture: |
-if phenocrysts (larger crystals) are found to occur as clusters of crystals |
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poikilitic texture |
-presence of a crystal which encloses another -can be helping in determining mineral crystallization |
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rapaki granite: |
hornblende-biotite granite containing large rounded crystals of orthoclase mantled with oligoclase |
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corona textures |
characterized by the presence of a rim of one of more crystals of a mineral around another mineral -can happen if pyroxene becomes unstable but doesn't totally dissolved |
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Inclusions: |
fragments of solid rock included in igneous rock |
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xenoliths |
"foreign rock" -if inclusions are unlike the host rock |
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autoliths |
-if inclusions are of same composition or directly related to host rock |
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vesicular texture |
if the rock contains numerous holes that were once occupied by a gas phase |
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amygdular texture |
if vesicles have been filled with material (usually calcite, chalcedony, or quartz) -a refilled vesicle |
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Paragenetic sequence: |
-describes the order in which mineral crystallization occurred in an igneous rock |
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bowers reaction series discontinuous branch: |
olivine -> pyroxene -> amphibole->biotite
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continuous branch: |
Ca-rich plagioclase ---> Na-rich plagioclase |
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last minerals in run series: |
k-feldspar -> muscovite -> quartz |
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As bowen rxn series goes down: |
silica content increases temp decreases resistance to weathering increases |
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Igneous differentiation: |
general term for the various processes by which magmas undergo bulk chemical changes |
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4 ways magmas change there composition: |
1.crystal fractionation 2. magma mixing 3. crustal assimilation 4. partial melting |
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Crystal fractionation, magma mixing, crustal assimilation: |
processes that take place with a magma or between different magmas |
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partial melting: |
occurs when a solid rock only partially melts, generating a magma different chemical composition from the original rock |
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fractional crystallization must have: |
a natural mechanism that can remove crystals from the magma or at least separate the crystals so that they can no longer react with the liquid |
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1.) Crystal settling/floating |
-if the crystals have a higher density than the magma, they will tend to sink or settle to the floor of the magma body (olivine, opaque minerals) -if the crystals have a lower density they will float of rise upward through the magma (plagioclase) |
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inward crystallization |
-Country rock which surrounds it magma is expected to be much cooler, heat will move outward away from the magma -the magma would be expected to crystallize from the walls inward |
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How are cumulate textures formed? |
-by the accumulation of crystals from a magma either by settling or floating |
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wheat is the Skaergaard intrusion |
-an intrusion in East Greenland -sited as a classic example of in-situ differentiation of magma -layer of olivine, layer of pyroxene -goes to mafic to more felsic -igneous layering related to density |
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The Bushveld Complex |
-worlds largest and most valuable layered intrusion -in South Africa -hosts over half the worlds platinum, chromium, vanadium and refractory minerals, and has Ore reserves -66,000 km^2 -has over 90% of the worlds reserves of PGM |
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PGMS: |
platinum group metals: -platinum, palladium, osmium, iridium, rhodium, and ruthenium |
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Magma Mixing |
-if 2 or more magmas with different chemical compositions come in contact with one another beneath the surface of the earth -it is then possible that they could mix with each other to produce compositions intermediate between end-members -not homogenized |
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what controls whether the magmas will mix completely? |
-temp -density -viscosity |
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What factors would tend to inhibit mixing: |
1.) temp contrast 2.) density contrast 3.) viscosity contrast |
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temperature contrast: |
basaltic and rhyolitic magmas have very different temps -if they come into contact with each other the basaltic magmas would tend to heat up and begin to dissolve any crystals that it had precipitated |
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Density contrast: |
-basaltic magma have densities -2600kg/m^3 -rhyolitic magmas have densities -2400kg/m^3 the contrast in density would mean that the lighter rhyolitic magmas would tend to float on the heavier basaltic magmas and inhibit mixing |
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Viscosity contrast: |
-basaltic magmas & rhyolitic magmas have very different viscosities -thus, some kind of vigorous stirring would be necessary to get the magmas to mix |
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evidence of magma mixing: |
1. mingling of magmas 2. disequilibrium mineral assemblages 3. reverse zoning in minerals |
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mingling of magmas |
we might expect to find rocks that show a "marble cake" appearance, with dark coloured magic rock intermingled with lighter coloured rhyolitic rock |
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disequilibirum mineral assembleges |
-if a basaltic magma containing Mg-rich olivine mixed with a rhyolite magma containing quartz and the magma was erupted before the quartz or olivine could be redissolved or made into another mineral, then we would produce a rock containing minerals that are that are out of equilibrium |
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reverse zoning in minerals |
-going back towards high temp chemical compositions ex. BSE image showing showing strong compositional zoning in olivine |
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-if mantle-derived magmas assimilate or are contaminated by crustal rocks then we would expect... |
-higher SiO2 content -crustal xenoliths (foreign rock) -lower MgO & FeO -higher incompatible trace elements -crustal signature of isotopes |
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how many degrees of freedom does a 1 component, 1 phase system have? |
2 degrees of freedom, b/c it can change its T and P independently |
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how many degrees of freedom exist in a in 2 phase system? |
1 degree of freedom b/c a change in T results in a change of P |
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Phase Rule: |
F=C-P+2
F: degree of freedom C: component P: phases |
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what happens to d.o.f when you increase the number of phases: |
it decreases |
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why is H2O is an unusual substance? |
b/c its liquid form is more dense then its solid form |
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what happens if we heat ice at pressures above the triple point? |
we go from ice to liquid to vapor
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what happens if we heat ice at pressures below the triple point? |
-we go from ice directly to vapour -sublimation! |
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Binary systems: |
systems with 2 components |
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Because we have an extra component, we: |
hold P constant at 1 bar |
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Isobaric phase rule: |
F=C-P+1 |
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If we have 3 phases present in a binary system, how many dof is there? |
F=2-3+1=0 -tells us the max number of phases that co-exist in an eqn. in a binary system is 3 |
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Melting point of pure diopside: |
1392 C |
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melting point of pure anorthite: |
1553 C |
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Eutectic temp: |
1274 C -where we get the first drop of liquid upon heating the sample (first melt!) |
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Eutectic composition: |
An42 Di58 |
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Observation #1 of diopside - anorthite binary phase diagram |
-all mixtures melt at the same temp -1st liquide to form in all mixtures have the same comp |
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#2 |
for mixtures >42% Di, all diopside melts and we are left with liquid and anorthite crystal |
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liquidus: |
temp at which the very last crystal is melting if you are heating the system |
