Mini Maxi Quiz Prep Flashcards
What are the conditions under which olivine is found
High temperature igneous material, common in mafic and ultra mafic rocks; commonly alters to serpentine
General formula for olivine?
(Mg,Fe,X)2SiO4
Formula for the olivine group
(Mg,Fe,Mn)2SiO4
Forsterite
MgSiO4
Fayalite
FeSiO4
What are neosilicates
Independent SiO4 tetrahedra; crystal sites or boxes
Some other names for olivine
Peridot- green gem
Chrysolite- yellow olivine
Dunite- solid, grainy masses of olivine. Classified as a rock
Olivinoid- extraterrestrial form of olivine found in meteorites
General garnet formula?
A2+ 3 B3+ 2 [SiO4]3
Which garnets make up the “pyralspites”
Pyrope MgAl, almandine Fe2+Al, spessartine MnAl
What are the 2 major groups of garnets
calcium rich and aluminum rich
which garnets make up the ugrandite series
uvarovite CaCr, grossular CaAl, andradite CaFe3+
Gore Mountain Garnet…
Pyrope-Almandine
What type of rock to garnets most occur in
metamorphic
where do pyralspites occur
meta-shales
where do ugrandites occur
meta-carbonates
Tsavorite Garnet is
grossular
Rhodolite is
pyrope-almandine
what controls the extent of substitution (solid solution)
TEMPERATURE
Aluminosilicates
Kyanite, Sillimanite, Andalusite (Al2SiO5)
how do these aluminosilicates form
moderate to high grade metamorphic minerals formed from AL-rich source rocks
General Aluminosilicate Formula
Al2SiO5 or AlO(Al,Si)O4
why do polymorphs form
Al position in the octahedral site or a mix of octahedral to tetrahedral sites
Al site location
Al can be in a six-coordination or four coordination site
High Pressure causes
more dense, packs MORE oxygen around Al3+
High Temperature causes
less dense, packs FEWER oxygens around Al3+
Sillimanite sites
octahedral and tetrahedral
kyanite sites
octahedral
Importance of these minerals?
- common in metamorphic rocks formed from shales (pelitic rocks). 2. Petrogenetic indicators
Mineral Solid Solution
A solid solution is a mineral structure where specific atomic sites are occupied in variable proportions by 2 or more different chemical elements
what are the 3 major controls on solid solution
atom size, valence charge, temperature
what needs to be true for substitution
the ionic radii of the substituting atoms must be able to fit into the site occupied by the entity for which they are substituting
radius ratio rule: if the atom in the middle is too small…
it will shake rattle and role
if the atom in the middle is too large…
a stable coordination shell will NOT form around it
rule of thumb for radius ratio
if the radii differ by 15-30% substitution is limited or very rare, if the radii differ by more than 30%, substitution is very unlikely
Paulings Rules
- coordination principle, 2. electrostatic valency principle, 3.sharing of polyhedral elements (geometry), 4.sharing of polyhedral elements (electric charges) 5. The Principle of Parsimony
What determines the shape of a molecule?
- electron pairs, bonding or nonbonding, repel eachother
- assume electron pairs are as far as possible from each other
Valence Shell Electron Pair Repulsion Theory (VSEPR)
The BEST energetic arrangement of a given number of electron domains is the one that MINIMIZES the repulsions among them
Electro Static Valence Principle
an ionic structure will be stable to the extent that the sum of the strengths of electrostatic bonds that reach an anion from adjacent cations= the charge of that anion (each atom the anion is sharing with must have same fraction of charge)
3rd rule:
The sharing of edges and particularly of faces of adjacent polyhedra tend to decrease the stability of an ionic structure
why is sharing important?
it yeilds POLYMERIZATION its how structures are built up
what type of sharing is the most stable
CORNER SHARING
what type of sharing is least stable
FACE SHARING
4th rule:
In a crystal with different cations those of high valence and small CN tend not to share polyhedral elements
5th rule:
the number of different kinds of constituents in a crystal tends to be small
shared corners in silicon tetrahedra are called?
bridging oxygens
pyroxene building blocks are modeled after what structure
I beam model
diopside formula
CaMgSi2O6
augite formula
Ca(Mg,Fe,Al)(Al,Si)2O6
general pyroxene formula:
W1-P(X,Y)1+PZ2O6 W= Ca Na X= Mg Fe2+ Mn Ni Li Y= Al Fe3+ Cr Ti Z= Si Al
because they are anhydrous
high temperature or dry conditions favor pyroxenes over amphiboles
Enstatite Formula
Mg2Si2O6 or MgSiO3
Ferrosilite
Fe2Si2O6 or Fe2+SiO3
Diopside
CaMgSi2O6
Hedenbergite
CaFe2+Si2O6
Jadeite
NaAlSi2O6
Aegerine
NaFe3+Si2O6
Ca-Tschermak
CaAl(Al,Si)O6
Miscibility gaps with the pyroxenes?
Clino v. Ortho and Ca-rich vs. Fe-Mg rich
orthopyroxenes
Ca-poor
between which 2 is there a Fe-Mg solid solution
Enstatite-Ferrosillite
Clinopyroxenes
Ca rich
between which 2 is there a Mg-Fe solid solution
diopside-hedenbergite
silicate tetrahedra chain linkages and cation size interact to produce
Pyroxenes and Pyroxenoids
the ionosilicate chain BLANK depending upon BLANK that fits within the bends of the silica tetrahedra
kinks, size of the cation
what is found in harrisville, ny
wollastonite and blue calcite
amphibole chemistry?
LARGE variety of chemical sites and sizes GREAT chemical range and a broad stability range
amphibole general formula
W0-1 X2 Y5 [Z8O22] (OH,F,CL)2 W= Na K X= Ca Na Mg Fe2+ (Mn, Li) Y= Mg Fe2+ Mn Al Fe3+ Ti Z= Si Al
What are the 5 amphibole sub-groups
Calcic Amphiboles, Sodic Clino-Amphiboles, (mg-Mn-Fe-Li) Clino Amphiboles, (Mg-Fe-Mn-Li) Ortho Amphiboles, Named Amphiboles
Mg-Ca-Na Solid solution of amphiboles?
tremolite, winchite, richterite
Cleavages of Pyroxenes v Amphiboles
pyroxene- 87 and 93
amphibole- 124 and 56
what are cleavage angles in these pyrox and amphi
weak bonds in M2 sites (around Ibeams instead of through them)
amosite?
asbestiform of cummingtonite-grunerite
Hornblende
a complex solid solution in a broad variety of both igneous and metamorphic rocks
sodic amphiboles
characteristic of high P/T subduction zone metamorphism- commonly called blueschist due to predominant bluish sodic amphiboles
crocidolite asbestos
asbestiform riebeckite
define plane
a two dimensional construct that defines a family of atoms within the crystal lattice. for example, the plane of basal obygen atoms or the plan of octahedral atoms
define sheet
a substructure consisting of a network of corner sharing tetrahedra or edge sharing octahedra
define layer
the combined sheets fundamental to the phyllosilicate group of minerals
Biopyroboles
Biotite Pyroxene Amphibole
whether or not a mineral or specific composition grows or remains in a rock depends on:
- Chemical composition of the geochemical system
- pressure of equilibrium reaction
- temperature of equilibrium reaction
reaction pathway complicated by
P-T-t gradients (pressure temp time) fluid composition (water co2) open/ closed hemical system deformation kinetics
