Earth Chemistry and Minerology

MatterMatter: anything that has mass and

volumeElement: substance composed of

atoms; can not be broken down 10 most common elements in Earth’s crust :

– Oxygen (O) - Silicon (Si)– Aluminum (Al) - Iron (Fe)– Calcium (Ca) - Sodium (Na)– Potassium (K) -Magnesium (Mg)– Titanium (Ti) - Hydrogen (H)

92 naturally occurring elements – the rest are made in a laboratory.

The Structure of an Atom

The nucleus is made up of the protons (positively charged molecules) and neutrons (no charge)– The number of protons and neutrons makes up the

atomic number

The electrons (negatively charged molecules) orbit, or circle, the nucleus.

Atomic number – equals number of protons

Symbol – one or two letter abbreviation

Name – elements common nameAtomic mass weighted average of all

isotopes

Periodic table – a tool used to organize information about the elements pp 688 + 689

What is a Mineral?

All rocks and minerals of Earth’s crust consist of elements

Mineral has the following characteristics:– Occurs naturally– Solid– Has a definite chemical composition– Its atoms are arranged in an orderly pattern– Inorganic (never alive)

4,000 known minerals

Eight most common elements found in in minerals:

Oxygen O - Calcium Ca– Silicon Si - Sodium S– Aluminum Al -

Potassium K– IronFe - Magnesium Mg

Most minerals are compounds

Minerals can form in several ways.1. Many form out of molten rock

Example: Granite

– 2. New minerals also form when existing minerals are transformed by heat, pressure or chemical action

Example: Hornblende Schist

3. Precipitation – solids form from super saturated solutions.

Ex calcite and halite

4. Hydrothermal solutions – dissolved elements react with each other in very hot water causing chemical reactions which form new minerals.

Structure of Minerals

Crystal: a regular geometric solid with smooth surfaces called crystal faces– By definition, all minerals have crystalline structures

(regular, orderly arrangements of atoms)

Crystal Structure:– The angle at which crystal faces meet is

characteristic for each type of mineral and can be used to help identify the mineral

– Six basic types of shapes

Cubic System

Orthorhombic System

Tetragonal System

Triclinic System

Hexagonal Structure

Monoclinic Stucture

Silicates:

Minerals that include compounds of silicon and oxygen.

More than 90% of the minerals in Earth’s crust are silicates

Silica tetrahedron: basic building block of a silicate

– Four oxygen atoms packed closely around a silicon atom

Crystal Structure and Physical Properties

The temperatures at which a mineral melts and vaporizes is individual to that mineral

Significance of crystal structure

Example of the relationship between hardness and crystalline structure: The following two minerals are both pure Carbon.– Diamond: Atoms arranged in tetrahedral

network – hardest natural mineral– Graphite: atoms arranged in sheets of

hexagonal networks – soft and flakes easily

Identifying MineralsMineralogy: study of minerals and

their properties

Minerals can be identified and classified by inspecting them visually and performing simple tests to determine their properties

Identifying Minerals by Inspection

Color the most easily observed propertyLeast useful for mineral ID

– Minerals may have similar colors

– Impurities and other factors can change colors

Calcite

Luster: the way the mineral shines in natural light

Metallic – shiny metal reflection

Non-Metallic

Non-metallic may shine like glass.

Testing Mineral Specimens

– Certain characteristics can be tested for.– Streak– Cleavage– Hardness– Specific gravity

StreakThe color of a mineral’s powder

Although the color of a mineral may vary, the streak rarely does

CleavageThe tendency to split along

definite planes– The planes along which the mineral splits

correspond to planes of weak bonds between atoms, ions or molecules

Fracture – If a mineral does not cleave, it fractures. An uneven breakage that can occur anywhere on the mineral.

HardnessHardness of a mineral is its resistance

to being scratched– Diamond: hardest of all minerals– Talc: softest of all minerals

Hardness of a mineral depends on: – arrangement of its ions, atoms or

molecules– strength of the chemical bonds between

them

Mohs Scale of Hardness

– 10 well-known minerals are assigned numbers 1-10

In most cases, a person can determine the approximate hardness of any common mineral by using your fingernail, a copper penny, a small glass plate and a steel file

Specific Gravity:

ratio of a minerals mass to the mass of an equal volume of water– Tells you how many times denser the mineral is

than water– Use a spring scale to measure

– Buoyancy: tendency of an object to float in water due to the differences in densities b/t the water and the object

Special Properties

Some minerals have unusual characteristics that can help ID the mineral

Taste like salt Magnetic propertiesReacts with HCl

Mineral Groups

SilicatesQuartz:

Chemical Formula: SiO2

Glassy or greasy lusterPure Quartz: colorlessColored Quartz: rose quartz, amethystHardness of 7 Significant component of many types of rocks

FeldsparsMake up about 60% of Earth’s crustShare 3 features:

– two directions of cleavage–Hardness of 6–Pearly luster

Most abundant family of mineralsImportant rock-forming mineralsUsed to manufacture glass and

ceramics

Other silicates

– Pyroxene: cleavage surfaces meet nearly at right angles

– Micas: soft silicates; hardness of 2.5 and perfect cleavage

– Amphibole: complex silicates; long, needlelike crystals

– Olivine: used to make jewelry– Kaolinite: aluminum silicate;

commonly used in ceramics, paints and fiberglass

Carbonates Minerals made of negatively charged

carbonate ions bonded to positive metal ions

All Contain CaCO3 –Calcium carbonate

All will effervesce with Hydrochloric acid HCl

Calcite and Dolomite

Calcite

Dolomite

Oxides

Mineral consisting of a metal element combined with oxygen

– Hematite and Magnetite

– Sulfides– Mineral consisting of a metal

element combined with sulfur

– Pyrite

Hematite

Magnetite

Pyrite

Native ElementsA group of minerals which

exist in pure form.Ex. Gold, silver, copper,

carbon