Physical Geology Introduction

Minerals - Building Blocks of Rocks


	a) crystalline solid - orderly internal 		

   	b) inorganic - not formed as part of a life 	

	c) fixed composition or variable between 	
	fixed limits

	d) naturally occurring - not a synthetic

States of Matter

Gas - lack of an internal arrangement - 

Liquid - short range order - 

Solid - non crystalline - short range order - 
liquid-like structure : glass, opal

Solid - crystalline - long range order - three-
dimensional Periodicity


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 

number of protons plus neutrons in the 

All elements have atoms which differ in N 
and are referred to as ISOTOPES

There are 92 so-called naturally occurring 

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 

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


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


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	


Transfer of electron(s) from one element to 
another (forming both a cation and an 
anion).  This „keeps¾ the ions together.


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 

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 

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


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 

  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


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 

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 

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