Minerals - Building Blocks of Rocks
Minerals
a) crystalline solid - orderly internal
arrangement
b) inorganic - not formed as part of a life
process
c) fixed composition or variable between
fixed limits
d) naturally occurring - not a synthetic
States of Matter
Gas - lack of an internal arrangement -
random
Liquid - short range order -
Solid - non crystalline - short range order -
liquid-like structure : glass, opal
Solid - crystalline - long range order - three-
dimensional Periodicity
Atoms
A Rigid Sphere about 1Angstrom in diameter
- an Angstrom is 10-10cm
Electrons are negative particles
At the center of an atom is a nucleus which
contains most of the mass of the atom
Protons with a positive charge
Neutrons with no charge - neutral
quarks and other interesting things
The ATOMIC NUMBER -Z- is the number of
protons in the nucleus
All atoms of the same CHEMICAL
ELEMENT have the same number of
PROTONS - Z.
The ATOMIC MASS NUMBER - N - the
number of protons plus neutrons in the
nucleus.
All elements have atoms which differ in N
and are referred to as ISOTOPES
There are 92 so-called naturally occurring
elements
Two of these elements are no longer found
on Earth
Elements with Z>92 are made in atomic
reactors at very high temperatures and they
decay rapidly
ELECTRONS - negatively charged particles
which orbit the nucleus
Neutral atoms have the same number of
protons as electrons
IONS are charged atoms - the charge results
from an addition to or subtraction from the
number of Electrons
CATIONS : the ion has a positive charge
therefore, there are more protons than
electrons - electrons have been removed
ANIONS : the ion has a negative charge
therefore, there are more electrons than
protons - electrons have been added
Electrons are distributed in specific orbits
around the central nucleus
The level closest to the nucleus is the K-shell,
followed by the L-shell, the M-shell and so
on.
Each of these shells is referred to as a
primary quantum level.
The maximum number of electrons in a level
increases away from the nucleus
Quantum No. Shell Max
1 K 2
2 L 8
3 M 18
n 2n2
Within each primary quantum level are
regions within which electrons cannot reside
If an electron falls from an outer level to a
level closer to the nucleus, energy is given off
- X-rays
CHEMICAL ELEMENTS
The Aufbau or build up principle
Start with a single proton - it is „balanced¾ by
a single electron in the K shell
This is the element Hydrogen - H
Add another proton. The second electron
enters the K shell which is now filled
This is the element Helium - He
Add a third proton - the third electron enters
the L shell and is further away from the
nucleus - This is the element Lithium - Li
The outer most electrons are the VALENCE
electrons. These electrons take part in
forming CHEMICAL BONDS between
elements to form COMPOUNDS (Minerals)
Elements with 8 valence electrons are quite
stable and only with difficulty form
compounds - the INERT GASES
PERIODIC PROPERTIES
Elements have properties which can be related
to their atomic number (number of protons in
the nucleus) and the distribution of electrons
around the nucleus.
Elements in the same column (group) have
similar characteristics...Group IA are all +1 ...
Group VIIIA are the Inert Gases
Chemical Bonding
IONIC BONDS
Transfer of electron(s) from one element to
another (forming both a cation and an
anion). This „keeps¾ the ions together.
COVALENT BONDS
Sharing electrons between two or more
elements : Carbon needs 4 valence
electrons and 2 Carbons can share 4
electrons each
Packing Models
Spheres of the same size cannot fill up all
space evenly
Open spaces remain when the most efficient
forms of packing are realized : Hexagonal and
Cubic Closest Packing : ~28% open space or
voids and 72% spheres
In these two packing schemes there are two
types of open spaces.
Tetrahedral Voids - an open space
surrounded by four nearest neighbors : a
pyramid made up of four equilateral
triangles
Octahedral Voids - an open space surrounded
by six nearest neighbors : an octahedron - an
eight-sided figure with each face an
equilateral triangle
If Oxygen anions form the framework, other
cations may be able to fit into the tetrahedral
or octahedral voids
Coordination Numbers
The smaller the cation, the smaller the
opening that it can fit into
2 fold - a linear arrangement
3 fold - a triangle
4 fold - a tetrahedron or a square
6 fold - an octahedron
8 fold - a cube
Some elements, like Aluminum, can fit into
two coordination schemes
Others, like Silicon prefer one scheme - a
tetrahedron
Temperature and Pressure can modify the
coordination numbers
Increasing pressure favors tighter packing:
increasing coordination - increasing density
Increasing temperature favors more open
packing : decreasing coordination -
decreasing density
Polymorphism
Compounds with the same composition but
different structures.
SiO2 - One Silicon and 2 Oxygens
4 6
SiO2 SiO2
quartz stishovite
Which phase is the high pressure form?
Which has the highest density?
Liquid Solution
Some liquids will mix in all proportions : gin
and milk. There are two end members (gin
and milk) and a mixture will have properties
that depend on how much of each end
member is added.
Other liquids will not mix - immiscible -
Solid Solution
Some solids will mix in all proportions and
others will not.
6 4 6 4
Mg2SiO4 Fe2SiO4
Olivine is the name given to all mixtures
between the Mg and Fe-rich end members.
Abundant Elements
Hydrogen and Helium are the two most
abundant elements in the universe
On Earth, element abundance is related to
the different spheres:
Atmosphere : Nitrogen (80%) & Oxygen
(19%)
Lithosphere : Continental Crust
Continental Crust
Element Wt% Size Packing
Oxygen - O 47% 1.4A
Silicon - Si 28% .4A 4 fold
Aluminum- Al 8% .5A 4,6 fold
Iron - Fe 5% .72A 6 fold
Calcium - Ca 4% 1.0A 8 fold
Sodium - Na 3% 1.0A 8 fold
Potassium - K 2.5% 1.4A 8 fold
Magnesium - Mg 2.1% .65A 6 fold
Physical Properties
Luster - appearance in reflected light
Cleavage - a structural controlled break
Fracture - non-structural controlled break
Density - mass/volume
Color - often function of impurities
Hardness - resistance to scratching
Moh's Hardness Scale
Relative Scale
10 - Diamond
9 - Corundum
7 - Quartz
6 - Feldspar : Glass/Knife Blade
5 - Apatite : Teeth
3 - Calcite : Fingernail
1 - Talc
Silicates
The fundamental structural unit is the silicon
and oxygen tetrahedron. The four oxygens sit
on the corners of the tetrahedon and the
silicon sits at the center.
These tetrahedra can be arranged in various
ways by sharing one or more oxygens
between adjacent tetrahedra.
There are some 3,500 recognized minerals
found on Earth.
For our purpose, we can focus on about a
dozen.
Silicates - Si, O and other elements
The most abundant mineral group in the
Earth's crust
Carbonates - Ca, Mg and CO3
Salts - NaCl
Silicate Minerals
The Silicon-Oxygen tetrahedron is the
fundamental structural unit. Oxygens occupy
the corners of the tetrahedron and the Silicon
sits at the center.
Silicates differ from each other as a function
of the extent of sharing oxygens with
adjacent tetrahedra.
Group Structure Composition
Olivine Isolated Fe and Mg
Pyroxene Single Chain Ca, Fe, and Mg
Amphibole Double Chains Ca, Fe, Mg
(with "OH")
Mica Sheet Silicates K, Na rich
(with "OH")
Plagioclase Tectosilicates Ca and Na rich
Alkali Tectosilicates Na and K rich
Feldspar
Quartz Tectosilicates Si
Silicates - Distribution
Olivine Mantle/Asthenosphere
Pyroxene Mantle/Asthenosphere
Amphibole Crust/Mantle
Mica Crust
Plagioclase Oceanic Crust
Alkali Feldspar Continental Crust
Quartz Continental Crust