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43 Cards in this Set

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  • Back
What is 2 theta?
The angle at which the x-ray reflects off a plane.
What is d-spacing?
The distance between two planes.
What can you determine from x-ray diffraction?
1.)Crystal structure - length of axes and angles btwn them
2.) sometimes mineral composition
3.) identify mineral(s)
4.) Est. volume %
What are the characteristics of the gold group?
-good conductors of heat & electricity
-malleable, ductile, sectile
-H= 2.5-3
-hackly fracture
-also wire like crystals & dendrites
Where do native elements of the gold group generally form?
Generally associated with igneous intrusions in hydrothermal veins
-Ag, Au often assoc. w/ felsic igneous plutons
-Cu can be felsic or mafic intrusions
What is a placer deposit?
Fine-grained deposits; minerals concentrated b/c of high SG and it is being weathered from igneous.
Name the 3 native elements with metallic luster.
Copper - Cu
Silver - Ag
Gold - Au
Name the 3 native elements without metallic luster.
Diamond, Graphite, and Sulfur
What is a sulfide?
-Sulfides are Fe, Cu, Zn, Pb, Mo bonded to sulfur.
-Often associated with metallic native element deposits.
-covalent and ionic bonds
-generally harder than native elements (except Mo)
Name some gold colored sulfides.
Pyrite - H=6-6.5
Chalcopyrite - H=3.5-4
Pyrrhotite - H=4
What is the coordination number?
The number of nearest neighbors about the ion/atom in the crystal structure
Framework silicates
All of the oxygens are bonded to 2 silicons.
(Si,Al)IV O2
What is a nesosilicate?
An individual tetrahedra silicate or orthosilicate.
1 Oxygen @ each corner and either a Si or Al in the center
What is a sorosilicate?
A double tetrahedra silicate. (Al,Si)2 O7
What is a Cyclosilicate?
A ring silicate.
Ex. Tourmaline
(Si,Al)6 O18
It looks like a star with six points
Why would hematite be less magnetic than magnetite?
-Magnetite has both Fe2+ and Fe3+, where hematite has only Fe2+
-Magnetite is Ferrimagnetic (magnetic moment not equal but opposite spins, one more powerful than the other
-Hematite has canted antiferromagnetic
What is an inosilicate?
Inosilicates are chain silicates. There are single chains (Si,Al)O3, eg. pyroxene, and double chains (Si,Al)4O11, eg. amphibole.
What is a phyllosilicate?
Phyllosilicates are sheet silicates. Eg. muscovite, biotite micas. (Si,Al)2 O5
There are Van der Waals bonds between the sheets. It is essentially numerous single or double chains or even bunches of rings attached in a sheet.
What are the two end members of Olivine made up of?
Mg2 Si O4 to Fe2 Si O4
How does the varied composition of olivine affect where it is seen?
Mg olivine crystallizes at a higher temp than Fe olivine. As a result, Mg olivine is seen in mafic and ultramafic rx and in meta-impure limestones and dolostones. Fe olivine is seen in felsic plutonic rx. Won't see Mg olivine w/ quartz, but can see Fe olivine with quartz.
Why do we see garnet in so many different rock types?
Because it has a wide range of compositions.
What are the 2 general types of garnets?
Ugrandite - Ca3 VIII (Al, Fe3+, Cr)2 VI Si3 IV O12 - seen in meta-impure limestones (white, green, cinnamon color)
Pyralspite - (Fe2+, Mg, Mn)3 VIII Al2 VI Si3 IV O12 - tends to be red, seen in all other rx
How does Gibbs Free Energy affect stability of a mineral in an assemblage?
The most stable phase or assemblage in a system has minimum Gibbs Free Energy.
What structure does a simple clay mineral have?
Continuous tetrahedral/octahedral sandwiches with nothing in between layers but Van der Waals bonds, It is a 1:1 clay
What is an example of a simple clay mineral?
-is a non-swelling clay
-occurs @ low Ph (acidic) from alteration of felsic minerals & rx.
What is an example of a 2:1 clay?
Illite. Non-swelling.
K <1 Al2 VI Si4 IV O10 (OH)2
Forms from alteration of micas & feldspar, has to be alkaline conditions so that there is K in solution
What is the basic structure of Illite, a 2:1 clay?
What is a dioctahedral clay and give examples.
A dioctahedral clay has a charge of +2 in the octahedral coordination (the six fold site). Kaolinite, Illite and some smectites can be dioctahedrals
What are the characteristics of smectite?
-a swelling clay mineral, sodium, calcium, + water allows for expansion.
-Glycol can make it expand more than water b/c it is bigger
-2:1 with Na, Ca, or H2O btwn
-forms from alteration of volcanic tuff & mafic minerals
What is the name of a dioctahedral smectite?
What is the name of a trioctahedral smectite?
-more likely from mafic minerals b/c need Mg
-has a charge of +3 in the VI-fold site
-VAC Al2 VI Si4 IV O10 (OH)2
-2:1 with K between
-dioctahedral mica
-add heat to get mica from clays
-K Al2 VI Si3 IV Al IV O10 (OH)2
What simple substitution gives you paragonite from muscovite?
K Al2 VI Si3 IV Al IV O10 (OH)2
+ Na K-1
=Na Al2 VI Si3 Al IV O10 (OH)2
This coupled substitution occurs in what minerals?
Ca Al IV Na-1 Si-1
Plagioclase feldspar, btwn anorthite and albite. micas btwn paragonite and margarite, pyroxene, amphibole
What is an example of a tri-octahedral mica?
What are the polymorphs of serpentine?
Chrysotile (most common form of asbestoform mineral)
What are the characteristics of Talc?
VAC Mg3 VI Si4 IV O10 (OH)2
-Van der Waals bonds btwn
What is an example of a 2:1:1 mineral?
-2 tetrahedral layers, 1 octahedral layer, 1 brucite layer
The Tet/Oct/Tet is a talc-like layer and the brucite layer is Mg3 (OH)6
What are the physical properties of pyroxene?
90 degree cleavage
2 types - monoclinic (CPX)and orthorhombic (OPX)
What is the generalized formula for pyroxene?
What are the physical properties of amphibole?
H= ~6
~60-degree cleavage
long & thin crystal form
prismatic or acicular
Why is there a miscibility gap between OPX and CPX?
Frequently see misc. gaps along Ca-Mg and Ca-Fe b/c Mg + Fe are bigger than Ca and don't substitute as easily. Mg-Fe do much better, closer in size.