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.

Elements and abundance in Crust

Element Weight %

Oxygen 46.6

Silicon 27.7

Aluminum 8.1

Iron 5.0

Calcium 3.6

Sodium 2.8

Potassium 2.6

Magnesium 2.1

98.5%

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

Example: Diagram a Lithium atom which has 3 protons, 3 electrons and 3 neutrons.

Questions:

What is the atomic mass of this atom?

What is the atomic number of this atom?

Is this atom NEUTRAL?

Does this atom have a stable electron configuration?

A Fluorine atom has an atomic number of 9 and an atomic mass of 19

Questions:

How many protons does the atom have

How many electrons does the atom have

How many neutrons does the atom have

Diagram the atom

Is the atom stable?

Is the atom neutral?

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

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

Other types of Bonds

Metallic bonding

Electrons move freely between ions acting as a “glue” which holds the ions together

Found in metals

van der Waals bonds

Molecules with a slight charge difference

Positive and negative side to molecule

Creates weakness in mineral (affects hardness)

Graphite and sulfur have this type of bond

Isotopes

An Element with differing number of neutrons…protons remain the same

How does this change the element?

Many elements have isotopes that don’t have stable nuclei

When an element’s nucleus decays it emits radioactivity (more on this next term)

Ex// C14 à N14

Why do we care about isotopes?

Used for age dating

Used for chemical analysis

Used to determine origin of magma

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?