GEO 303 Lecture Notes - Lecture 3: Nonmetal, Magnetochemistry, Feldspar

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10 May 2016
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Geo Minerals Lecture: Chapter 3 (Thurs: finish 3, start 5) Bring book to lab
Minerals-Outline
oWhat is a mineral?
Naturally occurring
Inorganic
Crystalline
Unique chemistry
oChemistry of minerals
Three layer earth
oEarth was struck multiple times by objects, initially the earth was a
giant ball of molten material. After a while, planetary differentiation
occurred, which separated materials by their weight. Why the core is
made of iron and nickel, lighter material goes to the surface, which
forms minerals.
oMinerals form because of different chemical reactions
The solid earth- made up of rocks
oRock-can be an aggregate of minerals and non-minerals, doesn’t have
to be specific
Three rock types
oIgneous rocks: crystalize from melts (magma)
oSedimentary rocks: form from sediments
oMetamorphic rocks: start with previous two, heat it up or pressure,
change it into this
oRocks come from minerals, and these types of minerals tell us how
they formed
Minerals
oMinerals: Naturally occurring substance that is a solid and inorganic
representable by a definite chemical formula, and an ordered atomic
structure
oQuartz: has a definite composition (SiO2)
So does Olivine (Mg, Fe) 2SiO4
(Me,Fe): can have either one, solid solution, doesn’t have a
fixed composition but varies between defined limits
oChemistry determined by element availability and charge balance
oCharge balance: chemistry determined by element availability
Quartz: (SiO2) SI^4 + 2 * O^-2= +4-4=0
Minerals need to be at a zero charge!
oMinerals have their atoms in a regular, repeating 3-D pattern
Unit cell: smallest, simplest 3-D piece of an ordered repeating
pattern
Will try to pack as close together as they can
oMineral polymorphism: ability for minerals with same composition to
crystalize with more than one structure
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Diamond is closely packed in, whereas Graphite is a different
shape and not as hard
oWhy the change?
Differences in pressure create different objects. Diamonds are
packed together at high pressure, whereas graphite is not.
Furthermore, because diamond is packed in tightly, and
graphite isn’t, its easier to break.
oIsostructural minerals: minerals with the same geometry or structure
but different chemistry
oCrystalline: orderly arrangement of atoms, proper circumstances
mean that they will form crystals, which is morphological
manifestation of the atomic arrangement,
oGeologists use physical features in order to determine the type of
mineral (Color, Size, Hardness, Shape, Cleavage: function of
arrangement of atoms and bond strength)
Iron or magnesium usually makes the minerals dark
Day 2: September 2nd
The strength of the bonds and the structure determines the cleavage, or how
the mineral will break
oIn general, crystals will break along the plains of their weakest bonds
Chemical Bonds
oAtoms and Elements
Nucleus
Protons and Neutrons
Protons have a positive charge
Protons determins the element
Has mass, atomic #
Neutrons
0 charge
Mass same as one proton
Atomic mass #
Doesn’t affect the weight?
Electron
In shells (2, 8, 8…)
Very little mass
Negatively charged
oPeriodic Table
Elements in order of atomic number (number of
protons)
Rows (Periods): # of electron shells
Columns (Groups): # electrons in outer shell
oIons
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