Geology 101/201 Mineral Lecture
Why should we care about minerals?
Economic and industrial value?
Educational and scientific value?
How can we tell one mineral from another?
Physical properties
Chemical properties
composition
atomic bonds
Why do minerals have different physical properties?
How do minerals form?
Magma
Recrystallization
Precipitation on earth’s surface
Minerals
Naturally occurring inorganic crystalline solid with a defined chemical composition.
Rocks are made of minerals
Minerals are made of elements
What is an Element?
Element: something that cannot be broken down into a more basic substance by ordinary chemical means.
What is an Atom?
Atom: The smallest individual particle that retains all the properties of an element.
Ex// an atom of iron (Fe)
3 basic particles that make up an atom
Protons
Charge: Positive 1
Mass: 1 atomic mass unit (amu)
Atomic Number: defines what the element is
Neutrons:
No charge (neutral)
Mass: 1 atomic mass unit (amu)
Electrons:
Negative 1 charge
No measurable mass
All atoms are neutral
What does this statement imply?
The atomic # is the Number of protons
How could we calculate the atomic mass of an atom?
Octet rule
Defines how the electrons fill the shells
Atomic shells fill from the inside out
Determines if the atom has a stable electron configuration
Octet Rule
Before an electron can go into the second shell there must be 2 electrons in the first shell
Before an electron can go in the third shell there must be 8 electrons in the second
Before an electron goes into the forth shell there must be 8 electrons in the third
This rule works until element #20
Only atoms that are neutral and stable are the noble gasses (family VIII on periodic table)
How can an atom become stable?
Atoms give up or take on electrons to fill their outer-most shell.
Lithium:
Neutral with 3 electrons but not stable
One electron in outermost shell
To become stable it gets rid of outermost electron
Is this now stable? Is it neutral?
IONS
Created when an atom takes on electrons or gives up electrons
Charged particle…no longer an atom because it is charged!
POSITIVE CHARGE: more protons than electrons
NEGATIVE CHARGE: more electrons than protons
Atoms give up or take on electrons based on which requires the least amount of energy.
Ion with a positive charge is a CATION
Ion with a negative charge is an ANION
In Class Exercise:
An atom has 5 protons and 6 neutrons
How many electrons does it have?
Diagram the atom
What is the atomic mass of the atom
What is the atomic number of the atom
Will the atom become a cation, anion or remain an atom? If it becomes an ion what will the charge be?
An atom has an atomic mass of 24 and it has 12 electrons
How many protons does it have? Neutrons?
Diagram the atom
Will the atom become a cation, anion or remain an atom? If it becomes an ion what will
the charge be?
Ionic Bonding
Stable and neutral compounds are created by joining cations and anions together
ex// Li+ and Fl- join to created LiFl
Ex// Na+ and Cl- join and create NaCl
This type of bonding is known as Ionic bonding
ions of opposite charges join together
Charge total must equal 0
Other ways to create stable elements?
Share electrons with another atom
Covalent bonding
Covalent bonding is created when atoms share electrons in the outer most shells
creates a molecule
Ex// Hydrogen has 1 electron
two hydrogen join by covalent bonding to complete the first electron shell
creates a hydrogen molecule
Covalent and ionic bonding creates stable and neutral molecules and compounds
Most minerals have covalent or ionic bonds or both
Chemical Formulas
What are chemical formulas and what do they tell us?
Each mineral is defined by a specific chemical formula
Quartz SiO2,
Halite NaCl,
Olivine (Mg,Fe)2SiO4
Solid solutions
A mineral that has a variation in composition between two end members
Olivine: (Mg, Fe)2SiO4
Varies between Mg end member and Fe end member
Feldspar
Polymorphs
Minerals with same chemical composition but different physical properties--> different mineral
Ex// Graphite and Diamond
Why do polymorphs occur?
Polymorphs form under different conditions
Graphite--> low pressure
Diamond--> high pressure
Says something about conditions of formation--> history of a region
Most Abundant elements in crust?
Oxygen (O) 46.6%
Silicon (Si) 27.7%
Aluminum (Al) 8.1%
Iron (Fe) 5.0%
Calcium (Ca) 3.6%
Therefore, most minerals are made up of what elements?
7 mineral groups
Each group is defined by a specific chemical constituent
First 6 groups make up the ore minerals
Last group is the rock forming minerals
Group 1 Carbonates
Carbonate ion (CO32-)
Calcite (CaCO3)
Malachite (CuCO3 (OH)2)
Carbonate ion combines with cation
Group 2 Oxides:
Oxygen ion (O2-)
ex// Hematite Fe2O3
Bauxite Al(OH)3
Oxygen combines with a metal
Group 3 Sulfides:
Sulfur ion (S2-)
ex//
Sulfur ion combines with a metal
Group 4 Sulfates:
Sulfate ion (SO42-)
ex// Barite (BaSO4)
Group 5 Halides:
A metal and non-metal ionically bonded
ex// Flourite (CaF2)
Group 6 Native elements:
(gold, silver, copper etc…)
Group 7 Silicates:
Silica tetrahedron (SiO4-)
Most common and abundant mineral group
Includes gemstones and most rock forming minerals
Silicate Structure is based on Silica Tetrahedron
1 silicon atom bonded covalently to 4 oxygen atoms
creates an anion with a -4 charge
Silicon has a +4 charge
Oxygen has a -2 charge
1 Si = +4 4O is -8 therefore net charge is -4
Ions attract due to different charges…bonding is covalent
Bonds with + charged ions to create stable compound
Or bonds with other tetrahedon
6 ways to bond silica tetrahedrons together (more in a minute)
Silicate Structures
Silicate minerals have different properties based on how the tetrahedrons join together
Silicate minerals have cleavage along ionic bonds
Silicate minerals have fracture along covalent bonds
Individual tetrahedron connected by cations
No cleavage only fracture
Example: Olivine
Ring Silicates (you don’t need to know this one)
Six tetrahedron joined together in a ring
Tetrahedron join together in chains (single chain silicates)
Chains are joined by cations
Two directions of cleavage at 90o
Pyroxenes
Tetrahedrons join together and create double chains
Double chains are joined by cations
2 cleavage planes that are at 60o and 120o
Amphiboles
Tetrahedrons join together and create sheets (sheet silicates)
Sheets are joined by cations
One cleavage plane
Tetrahedrons join covalently (framework silicates)
Primarily fracture
Feldspars Composition
Range in composition from calcium rich to potassium rich (solid solution)
Which feldspar forms is temperature dependent.
Plagioclase feldspar (anorthite-albite) Ca-Na rich
Orthoclase feldspar (microcline) K-rich
Forms of
Milky quartz
Rock quartz
Smoky quartz
Blue quartz
Citrine
Amethyst
Rose quartz
Tigers eye
Aventurine
Rutilated quartz
Forms of microcrystalline quartz
--Precipitated from solution
--Low temperature formation
Agate
Jasper
Onyx
Petrified wood
Carmelian
Chert
Opal
Silicate minerals and temperature
Bowen’s reaction series:
Shows at what temperature minerals will crystallize from a melt
Shows which minerals are found in which igneous rocks
Continuous vs discontinuous series