Minerals Minerals are the “building blocks” of rocks—hence,

Earth.

More than 4,000 are known.

Minerals Developed societies depend on mineral resources.

Metals – Iron, copper, lead, zinc, nickel, aluminum, etc.

Non-metals – Gypsum, limestone, aggregate, clay.

Minerals Economically important – Drive world economies.

Historically important – Dictated human history.

Iron.

Copper.

Gold.

Diamonds.

Gems.

Mineral Definition Geologic definition of a mineral is specialized:

Naturally occurring.

Solid.

Definite chemical

composition.

Ordered atomic

arrangement.

Mostly inorganic.

A mineraloid exhibits some of these properties.

Doesn’t include “minerals” in the nutritional sense.

Rocks Rocks are earth materials made from minerals.

Most rocks contain more than one kind of mineral.

Example: Granite

K-feldspar – Pink.

Quartz – Gray.

Hornblende – Black.

Some are monomineralic.

Limestone (Calcite)

Rock salt (Halite)

Glacial ice.

Atoms in a mineral are specifically ordered.

A solid with disordered atoms is called a glass.

Crystalline structure is based on atomic patterns.

Crystalline Structure

Crystals

Rare minerals displaying flat external faces.

Crystal faces form best in open cavities.

Crystals are often prized mineral specimens.

Crystals Constancy of interfacial

angles.

Different samples of the same mineral will have the same crystal faces.

Adjacent faces are always

oriented at the same angle.

Crystal faces reflect the

internal atomic order.

Crystal Lattice Ordered atoms in crystals form a 3-D lattice.

Lattices are patterns that repeat in three dimensions.

This internal pattern controls most mineral properties.

Crystal shape.

Symmetry.

Atomic Bonding

Lattice atoms are held in place by atomic bonds.

Bond characteristics also govern mineral properties.

Models depict atoms, bonds, and lattices.

Graphite

Polymorphs

Diamond

Minerals with the same composition; different structure.

Polymorphs reveal the importance of bond type.

Diamond and graphite are carbon polymorphs (C).

Diamond – Strong covalent bonds; hardest mineral.

Graphite – Weak van der Waals bonds; softest mineral.

Crystal Growth

Crystals grow as atoms attach to mineral surfaces.

Growth starts from a central seed crystal.

Growth expands outward as atoms accumulate.

Crystal Growth Outward crystal growth fills available space.

Resulting crystal shape is governed by surroundings.

Open space – Good crystal faces grow.

Confined space – No crystal faces.

Crystals grow by…

Solidification from a melt.

Precipitation from solution.

Solid-state diffusion.

Mineral Physical Properties

Pyrite

Characteristics determined by your five senses.

Used to ID minerals.

Properties depend upon…

Chemical composition.

Crystal structure.

Some are diagnostic.

Example: Pyrite (FeS2)

Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brassy color, sulfur smell when crushed, erroneously mistaken for gold (fool’s gold).

Minerals have unique sets of physical properties.

Mineral Physical Properties

Needle-like crystal habit

Common properties of

minerals are...

Crystal form.

Crystal habit.

Luster.

Color.

Streak.

Hardness.

Cleavage.

Fracture.

Specific gravity.

Mineral Physical Properties

Calcite effervesces with acid

Magnetite crystals on a large magnet.

Less common physical properties are... Taste.

Smell.

Feel.

Magnetism.

Effervescence.

Diaphaneity.

Piezoelectricity.

Pyroelectricity.

Refractive index.

Malleability.

Ductility.

Color

Quartz – Many colors Malachite – Always green

Color is diagnostic for some minerals.

Olivine is olive green.

Azurite is always blue.

Some minerals may exhibit a broad color range.

Quartz (Clear, white, yellow, pink, purple, gray, etc).

Color varieties often reflect trace impurities.

Streak

Hematite – Red-brown streak

Mineral color crushed on an unglazed porcelain plate.

Streak is often a useful diagnostic property.

Congruent streak – Streak color the same as the mineral.

Magnetite – Black mineral; black streak.

Incongruent streak – Streak color differs from the mineral.

Chromite – Black mineral; greenish-brown streak.

Luster

Satin spar Gypsum – Satiny luster

Quartz – Vitreous luster

The way a mineral surface scatters light.

Two subdivisions.

Metallic – Looks like a metal.

Nonmetallic.

Vitreous (glassy).

Satiny.

Silky.

Resinous.

Pearly.

Earthy (dull).

Adamantine (brilliant).

Resistance to abrasion (scratching)

Hardness compared to the Mohs hardness scale.

Hardness

Glass - Steel 5.5

Fingernail 2.5

Copper Penny 3.5

Steel File 6.5

Pyrite

Specific Gravity

Potassium Feldspar

Related to density (mass per volume)

Mineral weight over weight of equal water volume.

Specific gravity is “heft”– How heavy it feels.

Pyrite – Heavy (SG 5.0)

Feldspar – Light (SG 2.6)

Pyrite “feels” heavier than feldspar.

Crystal Habit Crystal habit is the ideal shape of crystal faces.

Ideal faces require ideal growth conditions.

Many descriptive terms are used to characterize habit.

Cubes Hexagonal PrismsBlades

Dodecahedra

Octahedra

Tetragonal PrismsRhombohedraCompound Forms

Crystal Form

Amethyst

Minerals vary in crystal face development.

Euhedral – Good crystal faces; grown in open cavity.

Anhedral – No crystal faces; grown in tight space.

Subhedral – Between the two.

Face development indicates growth history.

Anhedral crystals common; euhedral less so.

Cleavage Tendency to break along planes of lattice weakness.

Cleavage produces flat, shiny surfaces.

Described by the number of planes and their angles.

Sometimes mistaken for crystal habit.

Cleavage is through going; often forms parallel “steps”.

Habit is only on external faces.

1, 2, 3, 4, and 6 cleavages possible.

Examples of Cleavage:

1 direction

2 directions at ~ 90º

2 directions NOT at 90º

Cleavage Muscovite Mica

Amphibole

Potassium Feldspar

Examples of Cleavage:

Three directions at 90º

Three directions NOT at 90º

Cleavage

Calcite

Halite

Fracture

Obsidian Some minerals lack planes of lattice weakness.

Due to equal molecular bonds in all directions.

These minerals don’t cleave; they exhibit fracture.

Example: Quartz displays conchoidal fracture.

Shaped like the inside of a clam shell.

Breaks along smooth, curved surfaces.

Produces extremely sharp edges.

Mineral Compositions

74.3% of crustal minerals !!!

Only about 50 minerals are abundant.

98% of crustal mineral mass is from eight elements.

Oxygen O 46.6%

Silicon Si 27.7%

Aluminum Al 8.1%

Iron Fe 5.0%

Calcium Ca 3.6%

Sodium Na 2.8%

Potassium K 2.6%

Magnesium Mg 2.1%

All others 1.5%

Mineral Classes

Fluorite (Halide) Native CopperMalachite (Carbonate)

Minerals are classified based upon the dominant anion.

Silicates SiO24- Rock-forming minerals

Oxides O2- Magnetite, Hematite

Sulfides S- Pyrite, Galena

Sulfates SO42- Gypsum

Halides Cl- or F- Fluorite, Halite

Carbonates CO32- Calcite, Dolomite

Native elementsCu, Au, C Copper, Gold, Graphite

Silicate Minerals Silicates are know as “the rock-forming minerals.”

They dominate Earth’s crust.

Oxygen and silicon…

Make up 94.7% of crustal volume, and...

74.3% of crustal mass.

Silicate Minerals The anionic unit is the silica tetrahedron.

4 oxygen atoms are bonded to 1 silicon atom (SiO4

4-).

Silicon is tiny; oxygen is huge.

The silica tetrahedron has a net -4 ionic charge.

The silicate unit can be depicted by…

Spheres.

A ball-and-stick model.

Polyhedra.

Silicate Minerals

Type of Silicate Structure Formula Si:O Ratio

Independent Tetrahedra SiO4 0.25

Double Tetrahedra Si2O7 0.29

Ring Silicates Si6O18 0.33

Single Chains SiO3 0.33

Double Chains Si4O11 0.36

Sheet Silicates Si2O5 0.40

Framework Silicates SiO2 0.50

Silica tetrahedra link together by sharing oxygens.

More shared oxygen = lower Si:O ratio; governs…

Melting temperature.

Mineral structure and cations present.

Susceptibility to chemical weathering.

Independent Tetrahedra

KyaniteGarnet

Tetrahedra share no oxygens–they are linked by cations.

Olivine group.

High-temperature Fe-Mg silicate.

Small green crystals; no cleavage.

Garnet group.

Equant crystals with no cleavage.

Dodecahedral (12-sided) crystals.

Single-Chain Silicates

Pyroxene

Single-chain structures bonded with Fe and Mg.

Pyroxene Group.

Black-to-green color.

Two distinctive cleavages at nearly 90°.

Stubby crystals.

Augite is the most common pyroxene.

Double-Chain Silicates

Hornblende

Double chain of silica tetrahedra bonded together.

Contain a variety of cations.

Amphibole group - two perfect cleavages;

elongate crystals.

Sheet Silicates

Muscovite

Two dimensional sheets of linked tetrahedra.

Characterized by one direction of perfect cleavage.

Mica group – Biotite (dark) and Mucsovite (light).

Clay mineral group – Feldspar-weathering residue; tiny.

Framework Silicates

Potassium Feldspar

All four oxygens in the silica tetrahedra are shared.

Feldspar group – Plagioclase and potassium feldspar.

Silica (Quartz) group – Contains only Si and O.

Watermelon Tourmaline

Gems

Aquamarine Beryl

Minerals with special value.

Rarity.

Beauty.

Color.

Interaction with light.

Dispersion.

High refractive index.

Gems

Gems are cut and polished to be used in jewelry.

Facets are ground onto a gemstone by a machine.

Facets are not natural crystal faces.

Diamonds Diamonds originate under extremely high pressure.

~ 150 km deep (upper mantle).

Pure carbon is compressed into the diamond structure.

Rifting causes deep mantle rock to move upward.

Diamonds are found in kimberlite pipes.