How to identify a mineral 3

Minerals can be identified by their physical properties = atomic structure 5.. Identifying Minerals• Color: very variable, complex causes • Hardness: strength of atomic bonds • Density:

Minerals

Take-Away Points

1 Chemical elements form in stars

2 Atoms bond by sharing electrons

3 Minerals are classified by their chemistry

4 Minerals can be identified by their

physical properties = atomic structure

5 Silicates are the most important mineral

group

6 Crystals are determined by mathematical

rules called symmetry

Composition of the Sun

1 Chemical elements form in stars

Composition of the Sun

Iron, trailing off after

1 Chemical elements form in stars

How Elements Form in Stars

• Sun: 4 H  He

• He + particle  Mass 5 – Unstable

• He + He  Mass 8 – Unstable

• He + He + He  C

• Add more He to make heavier elements

• End of the line is iron for energy production

• Atoms beyond Iron made in massive stars

1 Chemical elements form in stars

What are Planets Made of?

• Same material as Sun

• Minus the elements that remain mostly in gases

• We find this pattern in a certain class of meteorites

1 Chemical elements form in stars

1 Chemical elements form in stars

The Earth’s Crust looks Very

Different

1 Chemical elements form in stars

Composition of the Crust

1 Chemical elements form in stars

Minerals are the Chemicals that

make up the Earth

Atomic Bonding

1 IONS

2 Atoms bond by sharing electrons

Atomic Bonding

2 Electrical Neutrality

• (+) and (-) Cancel Out

3 Bonding (Satisfy 1 & 2)

• Ionic (NaCl)

• Covalent (O2)

• Metallic (Cu, Al, Fe)

• Hydrogen (in water)

2 Atoms bond by sharing electrons

Ionic and Covalent Bonding

2 Atoms bond by sharing electrons

Metallic Bonding

2 Atoms bond by sharing electrons

Hydrogen Bonding

2 Atoms bond by sharing electrons

• Metallic bonding holds civilization together

• Hydrogen bonding gives water its

heat-retaining and solvent properties

2 Atoms bond by sharing electrons

5 Complex Anions (Radicals)

• Many minerals contain groups of atoms that behave as single units

2 Atoms bond by sharing electrons

Chemicals (and Minerals) Are

Classified by their Anions

3 Minerals are classified by their chemistry

For Example: Iron Compounds

Have Little in Common

• Fe: Gray, Metallic

• FeCl2: Light Green, Water Soluble

• FeSO4: Light Green, Water Soluble

• FeCO3: Brown, Fizzes in Acid

• FeS2: Dense, Brittle, Metallic, Cubic Crystals

3 Minerals are classified by their chemistry

On the Other Hand, Sulfides have Many Properties in

Minerals

4 Minerals can be identified by their physical properties

Identifying Minerals

• Color: very variable, complex causes

• Hardness: strength of atomic bonds

• Density: mass and spacing of atoms

• Luster: how electrons interact with light

• Cleavage: weak atomic planes

• Crystal Form: extremely useful but not for beginners

• Other properties distinctive at times

4 Minerals can be identified by their physical properties = atomic structure

Hardness

• Resistance to Scratching

• Directly related to relative strength of

atomic bonds

• Scratch Test (Mohs)

• Indentation Test (Knoop)

Common Errors due to:

• Weathering, ‘Chalk' marks

• Breaking vs Scratching

4 Minerals can be identified by their physical properties = atomic structure

Mohs vs Knoop Scales

1 Talc: very small

Density

• Directly related to masses of component

atoms and their spacing

• Usually very consistent

4 Minerals can be identified by their physical properties = atomic structure

Density - gm/cm3

(weight relative to water )

Wood - Balsa: 0.1, Pine: 0.5, Oak: 0.6-0.9

Gasoline: 0.7, Motor Oil: 0.9

Iridium: 22.4 (densest material on Earth)

4 Minerals can be identified by their physical properties = atomic structure

• Vitreous is often used for glassy luster

4 Minerals can be identified by their physical properties = atomic structure

Cleavage

• Tendency to split along smooth planes of

weaknessbetween atoms in crystal

• Directly related to atomic structure

• Related to Crystal Form

• Every cleavage face is a possible crystal face

• Not every crystal face is a cleavage face

Quartz commonly forms crystals but lacks

cleavage

4 Minerals can be identified by their physical properties = atomic structure

Other Properties

Crystal Form

• Takes Luck & Practice

• Well-formed crystals are uncommon

• Crystal Classification is somewhat subtle

Fracture

4 Minerals can be identified by their physical properties = atomic structure

Identifying Minerals

Geologic Setting

• Some minerals occur in all geologic

settings: quartz, feldspar, pyrite

• Some minerals occur mostly in sedimentary settings: calcite, dolomite

• Some minerals occur mostly in igneous

settings: olivine

• Some minerals occur mostly in

metamorphic settings: garnet, kyanite

4 Minerals can be identified by their physical properties = atomic structure

Identifying Minerals

Special Properties

• Taste, Magnetism, Etc

Experience and Reading

• “The best geologist is the one who’s seen the most rocks.”

4 Minerals can be identified by their physical properties = atomic structure

4 Minerals can be identified by their physical properties = atomic structure

A Common Example

Diffraction in Opal

4 Minerals can be identified by their physical properties = atomic structure

MAJOR MINERAL SUITES

Elements

Metallic:Au, Ag, Cu

• Not Al, Pb, Zn, Fe, etc

Nonmetallic: C - Diamond, Graphite

• Sulfur

4 Minerals can be identified by their physical properties = atomic structure

Copper Nugget

MAJOR MINERAL SUITES

Sulfides: Dense, Usually Metallic

Many Major Ores

MAJOR MINERAL SUITES

Halides: Usually Soft, Often Soluble

MAJOR MINERAL SUITES

Oxides: Often Variable, Some Ores

• Hematite Fe2O3

• Bauxite Al(OH) 3 (a hydroxide)

• Corundum Al2O3 (Ruby, Sapphire)

Carbonates: Fizz in Acid, Give off CO2

• Calcite CaCO3

• Dolomite CaMg (CO3)2

4 Minerals can be identified by their physical properties = atomic structure

MOST IMPORTANT MINERAL

Sorosilicates - Paired Tetrahedra

Epidote is the most common example

5 Silicates are the most important mineral group

Inosilicates - Chains

Single Chains (Pyroxenes)

5 Silicates are the most important mineral group

Inosilicates - Chains

Double Chains (Amphiboles)

5 Silicates are the most important mineral group

Phyllosilicates - Sheets

5 Silicates are the most important mineral group

• Serpentine (asbestos) minerals

5 Silicates are the most important mineral group

One Type of Asbestos

5 Silicates are the most important mineral group

Tectosilicates - Dimensional Networks

Three-• Quartz Feldspars

5 Silicates are the most important mineral group

Making Sense of Crystals

6 Crystals are determined by mathematical rules called symmetry

Unit Cells

All repeating patterns can be described in

terms of repeating boxes

The problem in Crystallography is to reason from the outward shape to the unit cell

6 Crystals are determined by mathematical rules called symmetry

Which Shape Makes Each Stack?

Crystals are determined by mathematical rules called symmetry

Stacking Cubes

6 Crystals are determined by mathematical rules called symmetry

Some shapes that result from

stacking cubes

6 Crystals are determined by mathematical rules called symmetry

Symmetry – the rules behind the shapes

6 Crystals are determined by mathematical rules called symmetry

Symmetry – the rules behind the shapes

6 Crystals are determined by mathematical rules called symmetry

The Crystal Classes

6 Crystals are determined by mathematical rules called symmetry

Take-Away Points

1 Chemical elements form in stars

2 Atoms bond by sharing electrons

3 Minerals are classified by their chemistry

4 Minerals can be identified by their

physical properties = atomic structure

5 Silicates are the most important mineral

group

6 Crystals are determined by mathematical

rules called symmetry