Minerals and Rocks. Why study minerals? Minerals are the building blocks of our planet. Any study of...

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Minerals and Rocks

Why study minerals?

Minerals are the building blocks of our planet.Any study of Earth’s material depends on an Understanding of minerals.

Industrial minerals are the source of raw for Manufacturing chemicals, concrete and wallboard.

Ore minerals are the source of valuable metals like copper and gold.

WHAT IS A MINERAL ?

A mineral is a homogenous, naturally occurring, solid inorganic substance with a definable chemical composition and an internal structure characterized by an orderly arrangement of atoms, ions, or molecules in a lattice.

Homogenous

Homogenous materials are the same through and through. They cannot physically broken into simpler components.

Naturally occurring

True minerals form by natural processes, not by the activity of a person.

A solid is a kind of matter that can maintain its Shape indefinitely and thus will not conform to the shape of its container.

Therefore liquids like oil and water and gases like air are not minerals.

Inorganic substance

Minerals do not contain organic chemicals.

An organic chemical consists of carbon bonded to Hydrogen along with varying amount of O, N and other elements.

Definable Chemical Composition

It it possible to write a chemical formula for a mineral.

Example:

Quartz has a chemical formula SiO2

Biotite:

K(Mg, Fe)3(AlSi3O10)(OH)2

The orderly arrangement of atoms in a lattice

Atoms are fixed in a specific pattern that repeats at regular intervals.

This orderly framework is called a crystal lattice.

Because minerals contain a crystal lattice, we say that they are crystalline

Minerals -----Elements ------ Atoms

The basic building blocks of minerals are chemical elements.

Element is a pure substance that cannot be separated into other elements.

112 elements are known at present.

The smallest piece of an element that has all the characteristics of an element is called the atom.

An atom consists of a nucleus

surrounded by a cloud of orbiting Electrons.

The nucleus is made up of protons and neutrons.

Electrons have a negative charge,protons have a positive charge,and neutrons have a neutral charge.

Individual electrons are located at given distances from the nucleus in regions called energy levels or shells.

Atomic Number: the number of protons in an atom of an element.

Atomic Weight: the approximate number of protonsplus neutrons in an atom of an element.

An atom that has the same number of electrons as protonsis said to be neutral. It does not have an overall electric charge.

An atom that is not neutral is called an ion.

An ion that has an excess negative charge is anion.

An ion that has an excess positive charge is called cation.

Molecule: two or more atoms bonded together. The atoms May be of the same element or of different elements.

Compound: Elements combine with each other. A compoundConsists of two or more elements bonded together in definiteProportions.

The mass number of an atom is defined as the total of its neutrons and protons in the nucleus.

Some elements have more than one mass number: samenumber of protons but different number of neutrons.

These kind of elements are called isotopes.

Carbon

carbon-12six protons + six neutrons

carbon-14six protons + eight neutrons

Some isotopes are unstable.

Unstable means that the isotope disintegrate through a process called Radioactive Decay.

PROPERTIES OF MINERALS:

How do we tell one mineral from the another ?

Definable chemical composition and specific crystallinestructure of a mineral controls its

physical properties.

Common Physical Properties of Minerals:

ColorStreakLusterHardnessCleavageSpecific Gravity

Colors results from the way a mineral interact with light.

Certain minerals always have the same color: e.g. galenais always gray.

Quartz

fluorite

come asmany different colors

ANALCIME REALGAR CROCOITE TYUYAMUNITE

MALACHITE TURQUOISE CAVANSITE AZURITE

FLUORITE AMETHYST KAEMMERERITE BIXBYITE

STREAK

The streak of a mineral refers to the color of its powder.

LUSTER

Luster refers to the way a mineral surface scatters light.

Mineral that have the appearance of metals, are metallic: Pyrite

Non-metallic minerals can have silky, glassy, pearly or earthy luster.

Metallic Luster

Waxy Luster

Silky Luster

Pearly Luster

Sub metallicLuster

VitreousLuster

HARDNESS

Hardness is a measure of relative ability of a mineral toresist scratching, and therefore the resistance of bonds in the lattice to being broken.

Hardness is one of the most useful diagnostic properties of minerals.

Friedrich Mohs in the early 1800s listed some mineral in sequenceof relative hardness. A mineral with a hardness of 5 can scratchAll minerals with a hardness of 5 or less.

1010 DiamondDiamond

99 CorundumCorundum

88 TopazTopaz

77 QuartzQuartz

66 K-feldsparK-feldspar

55 ApatiteApatite

44 FluoriteFluorite

33 CalciteCalcite

22 GypsumGypsum

11 TalcTalc

Hardest

Softest

Mohs HarnessMohs HarnessScaleScale

TalcH=1

GypsumH=2

ApatiteH=5

TopazH=8

DiamondH=10

• Finger Nail (H = 2.5)

• Penny (H = 3)

• Knife Blade (H = 5.5)

You typically do not carry around a supply of the 10 minerals on the hardness scale:

CLEAVAGE

A mineral cleavage is the way it breaks.Minerals tend to break where the bonds holding the Atoms together in the crystal are the weakest.

When they break, a series of surfaces parallel to these Bonds may form; the surfaces are called cleavage planes.

Some minerals have one cleavage plane like mica.

Some minerals have two or three cleavage planes thatintersects at a specific angle.e.g. Halite has three sets at 90 degrees.

Specific gravity is a measure of the density of a mineral. At times it is such a useful property that it is the only way to distinguish some minerals without laboratory or optical techniques.

Gold can easily be distinguished from Pyrite "fool's gold" by specific gravity alone.

Specific Gravity (SG)

Specific gravity is a unitless measure, because it is derived from the density of the mineral divided by the density of water

If a mineral has a SG of 2, then it is twice as dense as water.

Mineralogists distinguish several principal classes of mineralsbased on their chemical composition:

4000 minerals have been identified. However, they can be separated into a relatively small number of groups, or mineral classes.

SilicatesOxidesSulfidesSulfatesHalides

CarbonatesNative Elements

Only a few minerals make up most of the Earth’s crust. These minerals are called Rock Forming Minerals.

Only eight minerals make up the bulk of these mineralswhich represents 98 percent of the continental crust.

These elements are: Oxygen (O) 46.6 %Silicon (Si) 27.7 %Aluminum (Al)Iron (Fe)Calcium (Ca)Sodium (Na)Potassium (K)Magnesium (Mg)

Oxygen and Silicon are the most abundant elements.

They combine together to form a Silicon-Oxygen

Tetrahedron

which is the framework of the most common group of minerals:

Silicates

One Silicon atom

Four oxygen atoms

Silicon-Oxygen tetrahedron is the fundamental Component of silicates.

A tetrahedron is a pyramid-like shape with four triangular faces.

Olivine Single Tetrahedron

Pyroxene Single Chain

Amphibole Double Chain

Micas Sheets

Feldspars

Quartz

Three-dimensionalframework

The Oxygen-silicon tetrahedra are connected to one another by other elements such as Fe, Mg, Ca or K.

Quartz and feldspars are very important minerals in geology because they are the most abundant minerals in the crust.

and Orthoclase

The two most common type of feldspars are:Plagioclase

Non-Silicates:

Oxides: Metal cations bonded to oxygen

Hematite is Fe2O3

Oxides are commonly rich in metals, so they are used as ore mineralsand have economic values.

Non-Silicates:

Sulfides: Metal cations bonded to sulfide (the anion of sulfur).

Galena is PbS

Pyrite is FeS2

Sulfides are also used as ore minerals.

Non-Silicates:

Sulfates: metal cation bonded to SO4 2-

Gypsum is a sulfate.

Non-Silicates:

Halides: a halogen ions (elements from the secondcolumn from the right in the periodic table) such as Cl bonded to a cation

Halite or rock salt

Flourite

Non-Silicates:

Native elements: pure masses of a single element (metals andnon metals)

Copper (Cu)

Graphite (C)

Non-Silicates:

Carbonates: carbon plus oxygen plus other elements

The most common group after silicates

Calcite Dolomite

• Igneous rocks

• Sedimentary rocks

• Metamorphic rocks

Characteristics of magma

• Igneous rocks form as molten rock cools and solidifies

• Characteristics of magma (molten rock)• Parent material of igneous rocks• Forms from partial melting of rocks

inside the Earth• Magma that reaches the surface is lava

• General Characteristic of magma• Rocks formed from lava at the surface are

classified as extrusive, or volcanic rocks• Rocks formed from magma that

crystallizes at depth are termed intrusive, or plutonic rocks

Extrusive Igneous Rock - Lava (Hawaii)

Intrusive Igneous Rock (Granite)

• The nature of magma• Consists of three components:

– A liquid portion, called melt, that is composed of mobile ions

– Solids, if any, are silicate minerals that have already crystallized from the melt

– Volatiles, which are gases dissolved in the melt, including water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)

• Crystallization of magma• Cooling of magma results in the

systematic arrangement of ions into orderly patterns

• The silicate minerals resulting from crystallization form in a predictable order

Crystallization of minerals in magma bodies

• Bowen’s reaction series and the composition of igneous rocks

• N.L. Bowen demonstrated that as a magma cools, minerals crystallize in a systematic fashion based on their melting points

Bowen’s Reaction Series

• Crystallization of magma• Texture in igneous rocks is determined by the

size and arrangement of mineral grains• Igneous rocks are typically classified by both:

– Texture

– Mineral composition

Igneous textures

• Texture is used to describe the overall appearance of a rock based on the size, shape, and arrangement of interlocking minerals

• Factors affecting crystal size• Rate of cooling

– Slow rate promotes the growth of fewer but larger crystals

Igneous textures

• Factors affecting crystal size • Rate of cooling

– Fast rate forms many small crystals

– Very fast rate forms glass

• Amount of silica (SiO2) present

• Amount of dissolved gases

Types of Igneous textures• Types of igneous textures

• Aphanitic (fine-grained) texture– Rapid rate of cooling of lava or magma– Microscopic crystals– May contain vesicles (holes from gas bubbles)

• Phaneritic (coarse-grained) texture– Slow cooling– Crystals can be identified without a

microscope

Aphanitic texture

Phaneritic texture

Igneous textures

• Types of igneous textures• Porphyritic texture

– Minerals form at different temperatures as well as differing rates

– Large crystals, called phenocrysts, are embedded in a matrix of smaller crystals, called the groundmass

• Glassy texture– Very rapid cooling of molten rock– Resulting rock is called obsidian

Porphyritic texture

Granite

Glassy texture

Obsidian

More types of Igneous textures

• Types of igneous textures• Pyroclastic texture

– Various fragments ejected during a violent volcanic eruption

– Textures often appear to more similar to sedimentary rocks

• Pegmatitic texture– Exceptionally coarse grained– Form in late stages of crystallization of

granitic magmas

Pyroclastic Rock

Summary - Igneous Rock Classification

Summary - Igneous Rock Texture and Composition

What is a sedimentary rock?• Sedimentary rocks result from

mechanical and chemical weathering• Comprise ~ 5% of Earth’s upper crust• Contain evidence of past environments

• Record how sediment is transported• Often contain fossils

Fossil Fish - 50 Million Year Old Lakes in southern Wyoming

Sediment is fine-grained mudstoneSediment is fine-grained mudstone

Turning sediment into rock

• Changes occur in sediment after it is deposited

• Diagenesis – chemical and physical changes that take place after sediments are deposited

Turning sediment into rock

– Diagenesis– Recrystallization – growth of stable minerals

from less stable ones

– Lithification – loose sediments is transformed into solid rock by compaction and cementation

– Natural cements include calcite, silica, and iron oxide

Types of sedimentary rocks

• Detrital rocks – transported sediment as solid particles

• Chemical rocks – sediment that was once in solution

Detrital sedimentary rocks

• Constituents of detrital rocks can include• Clay minerals

• Quartz

• Feldspars

• Micas

• Particle size is used to distinguish among the various types of detrital rocks

• Common detrital sedimentary rocks (in order of increasing particle size)

• Shale– Mud-sized

particles deposited in thin layers called laminae

• Sandstone

• Conglomerate and breccia

– Both composed of particles > 2mm in diameter

– Conglomerate consists largely of rounded clasts

– Breccia is composed of large angular particles

Chemical sedimentary rocks

• Precipitated material once in solution

• Precipitation of material occurs two ways:• Inorganic processes• Organic processes (biochemical origin)

• Common chemical sedimentary rocks• Limestone

– Most abundant chemical rock

– Made of the mineral calcite

– Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms)

– Inorganic limestones include travertine and oolitic limestone

Coquina

Fossiliferous limestoneNote shells and lime matrix

Chalk Outcrops in SE USA

Chalk Hand Specimen

Oolitic Limestone - Bahama Shoals

Oolitic Limestone - Hand Specimen

Ooids under microscope

Travertine forming in Hot Spring

Travertine Hand Specimen

Chemical sedimentary rocks• Common chemical sedimentary rocks

• Dolostone– Typically formed secondarily from limestone

– Common in ancient rocks, rare today

• Chert– Made of microcrystalline quartz

– Usually deposited as siliceous ooze in deep oceans (can be diatomaceous)

chert Diatomaceous chert

• Common chemical sedimentary rocks• Evaporites

– Evaporation triggers deposition of chemical precipitates

– Examples include rock salt and rock gypsum

• Common chemical sedimentary rocks• Coal

– Different from other rocks because it is composed of organic material

– Stages in coal formation (in order)

» 1. Plant material

» 2. Peat

» 3. Lignite

» 4. Bituminous

Metamorphic Rocks

• The transformation of rock by temperature and pressure

• Metamorphic rocks are produced by transformation of:

• Igneous, sedimentary and igneous rxs

Metamorphism

• Metamorphism progresses from low to high grades

• Rocks remain solid during metamorphism

What causes metamorphism?

• Heat• Most important agent • Heat drives recrystallization - creates new,

stable minerals• Pressure (stress)

• Increases with depth• Pressure can be applied equally in all

directions or differentially

Origin of pressure in metamorphism

Metamorphism

• Three types of metamorphic settings:• Contact metamorphism – from a rise in

temperature within host rock• Hydrothermal metamorphism – chemical

alterations from hot, ion-rich water• Regional metamorphism -- Occurs in the

cores of mountain belts and makes great volumes of metamorphic rock

Contact metamorphism

Produced mostly by local heat source

Metamorphism and plate tectonics

• Most regional metamorphism occurs along convergent plate boundaries

• Compressional stresses deform plate edge• Occurs in major mountain belts: Alps,

Himalayas, and Appalachians

Index Minerals in metamorphic rocks

Metamorphic Environments

• Metamorphic grade• A group of minerals that form in a

particular P-T environment

Zeolite (really low T,P; <200C)Greenschist (low T, P; 200-450C, 10-15 km)Blueschist (low T, high P - subduction zones)Amphibolite (high T, P; 450-650C, 15-20 km)Granulite (super high T, P; >700C, >25km)

Common metamorphic rocks

• Nonfoliated rocks• Quartzite

– Formed from a parent rock of quartz-rich sandstone

– Quartz grains are fused together

– Forms in intermediate T, P conditions

• Nonfoliated rocks• Marble

– Coarse, crystalline

– Parent rock usually limestone

– Composed of calcite crystals

– Fabric can be random or oriented

• Foliated rocks• Slate

– Very fine-grained

– Made by low-grade metamorphism of shale

• Foliated rocks• Phyllite

– Grade of metamorphism between slate and schist

– Composed mainly of muscovite and/or chlorite

• Foliated rocks• Schist

– Medium- to coarse-grained

– Comprised of platy minerals (micas)

– The term schist describes the texture

• Foliated rocks• Gneiss

– Banded appearance

– High-grade metamorphism

– Composed of light-colored feldspar layers with bands of dark mafic minerals

What are metamorphic textures?

• Texture refers to the size, shape, and arrangement of mineral grains within a rock

• Foliation – planar arrangement of mineral grains within a rock

Outcrop of foliated gneiss

The rock cycle

- Series of processes by which rocks changes into other types of rocks

- Illustrates various processes and paths as earth materials change both on the surface and inside the Earth

- What are the three main rocks ? 1- Igneous

2- Metamorphic 3- Sedimentary

The rock cycle

Fundamental Rock Types

- Igneous Rocks: solidify from melt, e.g. lava (extrusive) or magma (intrusive)

- Sedimentary Rocks: are made at the Earth’s surface from particle and chemical remnants of other rocks

- Metamorphic rocks: form when other rocks are heated, squeezed, and deformed.

Minerals and Rocks. Why study minerals? Minerals are the building blocks of our planet. Any study of...

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