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Matter and Minerals

Chapter 1 Lecture

Natalie Bursztyn

Utah State University

Foundations of Earth Science

Eighth Edition

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List the main characteristics that an Earth material must possess to be considered a mineral.

Describe each characteristic.

Focus Questions 1.1

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Minerals are the building blocks of rocks

Study of minerals is mineralogy

Minerals important in human history

Flint and chert for weapons and tools

Gold, silver, and copper mined by Egyptians

Bronze developed by 2200 b.c.

Mining became common by the Middle Ages

Minerals: Building Blocks of Rocks

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Geologists’ definition:

Naturally occurring

Inorganic solid

Orderly crystalline structure

Definite chemical composition

Defining a Mineral

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Minerals are naturally occurring

Form by natural geologic processes

Synthetic materials are not considered minerals

Defining a Mineral

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Minerals are generally inorganic

Crystalline solids from organic sources are generally not considered minerals

Some organisms secrete inorganic compounds like calcium carbonate

Considered a mineral when they become part of the rock record

Defining a Mineral

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Minerals are solid substances

Ice (frozen water) is considered a mineral

Liquid water and water vapor are not

Defining a Mineral

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Minerals have an orderly crystalline structure

Atoms are arranged in an organized, repetitive manner

Organization is reflected in the crystal shape

Defining a Mineral

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Minerals have a chemical composition that allows for some variation:

Most minerals are compounds

Can be expressed as a chemical formula

Example: quartz = SiO2

Composition may vary slightly if certain elements substitute for others

Substituting elements about the same size will not change the crystalline structure of the mineral

Defining a Mineral

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A rock is a naturally occurring solid mass of mineral, or mineral-like matter

Most are aggregates of several different minerals

Individual properties of the minerals are retained

Some rocks are composed of a single mineral

Example: limestone is an impure mass of the mineral calcite

Some rocks are made of non-mineral matter

Examples: obsidian and pumice (volcanic glass), coal (organic)

What is a rock?

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What is a rock?

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Compare and contrast the three primary particles contained in atoms.

Focus Question 1.2

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All matter — including minerals — is composed of atoms

An atom is the smallest particle that cannot be chemically split

Atoms contain even smaller particles:

Protons

Neutrons

Electrons

All atoms (excluding H and He) formed inside massive stars by nuclear fusion

Atoms: Building Blocks of Minerals

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Protons, Neutrons, and Electrons:

Protons and neutrons have almost identical masses

Electrons are much smaller (1/2000) than protons and neutrons

Protons have a charge of +1

Neutrons have no charge

Electrons have a charge of 1

Most matter is neutral, because the charges of protons and electrons cancel each other out

Atoms: Building Blocks of Minerals

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Electrons are sometimes shown orbiting the nucleus like planets in a solar system

Electrons actually surround the nucleus like a cloud

Atoms: Building Blocks of Minerals

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Electrons:

Move around the nucleus in a cloud with different regions called principle shells

Each principle shell has an energy level and a specific number of electrons

The outer shell contains valence electrons

Interact with valence electrons of other atoms to form chemical bonds

Atoms: Building Blocks of Minerals

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The number of protons in the nucleus of an atom gives its atomic number

Determines chemical nature of atom

All atoms with the same atomic number are known as an element

Approximately 90 naturally occurring elements

Elements are arranged in the periodic table

Elements with similar properties line up in columns

Elements: Defined by Their Number of Protons

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Elements: Defined by Their Number of Protons

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Most minerals are chemical compounds

Two or more elements joined together

A few minerals are made up of single elements

Native minerals

Elements: Defined by Their Number of Protons

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Distinguish among ionic bonds, covalent bonds, and metallic bonds.

Focus Question 1.3

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Elements (excluding noble gasses) form bonds under the temperature and pressure conditions that occur on Earth

Bonds lower the total energy of the atoms and make them more stable

Why Atoms Bond

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Eight valence electrons is a stable arrangement and a full valence shell

The noble gasses all have full valence shells so they lack chemical reactivity

Elements gain, lose, or share electrons during chemical reactions

Producing stable electron arrangements

The Octet Rule and Chemical Bonds

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The Octet Rule

Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons

The Octet Rule and Chemical Bonds

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A chemical bond is the transfer or sharing of electrons that results in a full valence shell

Ionic bonds: electrons are transferred

Covalent bonds: electrons are shared

Metallic bonds: electrons move around

The Octet Rule and Chemical Bonds

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When one atom loses or gains valence electron(s), ions are formed

Electrons are lost: becomes a positive ion

Electrons are gained: becomes a negative ion

Ionic bonds form when ions with opposite charges are attracted

Creates ionic compounds

Ionic Bonds: Electrons Transferred

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NaCl is an ionic compound

Na loses a valence electron (becomes positive)

Cl gains a valence electron (becomes negative)

Ionic Bonds: Electrons Transferred

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Ionic compounds have very different properties than the bonded elements that make them up

Example: Sodium Chloride

Sodium

Soft, silver, toxic metal that reacts explosively when exposed to water

Chlorine

Poisonous green gas used as a chemical weapon during World War I

Sodium Chloride is table salt!

Ionic Bonds: Electrons Transferred

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A covalent bond forms when electrons are shared between atoms

Covalent Bonds: Electron Sharing

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Metallic bonds form when valence electrons are free to move from one atom to another

All atoms share available valence electrons

Movement of valence electrons between atoms results in:

High electrical conductivity

Malleability

Other unique properties of metals

Metallic Bonds: Electrons Free to Move

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List and describe the properties used in mineral identification.

Focus Question 1.4

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Minerals have a definite crystalline structure and chemical composition

Gives them unique physical and chemical properties

Physical properties of individual samples may vary due to impurities and defects

Diagnostic properties are useful in identifying unknown minerals

Ambiguous properties vary among different specimens of the same mineral

Properties of Minerals

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Luster is the quality of light reflected from the surface of a mineral

Minerals that look like shiny metal have a metallic luster

A submetallic luster appears slightly dull

Nonmetallic luster includes:

Vitreous or glassy, dull or earthy, pearly, silky, and greasy

Optical Properties

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Color may be one of the most conspicuous properties of a mineral, but it is only a diagnostic property for a few minerals

Slight impurities in the chemical composition of a mineral can change the color dramatically

Optical Properties

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Streak is the color of a mineral in powdered form

Obtained by rubbing the sample on an unglazed porcelain tile known as a streak plate

Streak, unlike color, is generally consistent

Metallic minerals generally have a dense, dark streak

Nonmetallic minerals generally have a light streak

Not all minerals produce a streak

Optical Properties

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Optical Properties

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Ability to transmit light

Minerals that do not transmit light are opaque

Minerals that transmit some light, but not an image, are translucent

Minerals that transmit both light and images are transparent

Optical Properties

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Crystal shape or habit is the characteristic shape of individual mineral crystals or aggregates of crystals

Most minerals grow in one common shape, but some have two or more characteristic shapes

Crystal Shape or Habit

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Crystal Shape or Habit

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Crystal Shape or Habit

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The strength of a mineral is determined by the strength of its chemical bonds

Mineral strength determines how minerals break or deform under stress

Mineral Strength

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Hardness is a mineral’s resistance to abrasion or scratching

Hardness is measured on a scale of 1 to 10 (Moh's Scale)

Can be determined by rubbing the mineral against a material of known hardness

Fingernail (hardness = 2.5)

Copper penny (hardness = 3.5)

Glass (hardness = 5.5)

Mineral Strength

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Mineral Strength

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Mineral Strength

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Cleavage is the tendency of a mineral to break along planes of weak bonding

This produces smooth, flat surfaces where the mineral is broken

Not all minerals have cleavage

Cleavage can be easily confused with crystal shape

Remember that cleavage is visible when a mineral is broken

Mineral Strength

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Mineral Strength

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Mineral Strength

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Fracture is a property resulting from chemical bonds that are approximately equal in strength

Irregular fracture: uneven broken surface

Conchoidal fracture: smooth, curved broken surface

Some minerals exhibit splintery or fibrous broken surfaces

Mineral Strength

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Mineral Strength

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Tenacity is a mineral’s resistance to breaking, bending, cutting, or deforming

Minerals with ionic bonds tend to be brittle

They will shatter

Native metals are malleable

They can be hammered without breaking

Sectile minerals can be cut into thin shavings

Elastic minerals will return to their original shape after being bent

Mineral Strength

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Specific gravity describes the density of a mineral

Ratio of a mineral’s weight to the weight of an equal volume of water

Most minerals have a specific gravity between 2 and 3

Many of the metallic minerals have a much higher specific gravity (20 for gold)

Can be estimated by hefting a mineral in your hand

Density and Specific Gravity

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Some minerals have distinctive properties:

Taste (halite is salty)

Feel (talc is soapy; graphite is greasy)

Smell (sulfur smells like rotten eggs)

Magnetism (some can be picked up by a magnet and some can pick up iron objects)

Optical properties (calcite refracts light)

Effervescence (carbonate minerals fizz when exposed to dilute acid)

Other Properties of Minerals

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Other Properties of Minerals

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List the common silicate and nonsilicate minerals.

Describe what characterizes each group.

Focus Questions 1.5

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There are over 4000 named minerals, but only a few dozen are abundant in Earth’s crust

Known as rock-forming minerals

Economic minerals are less common than rock-forming minerals but are used extensively in the manufacture of products

Mineral Groups

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The majority of rock-forming minerals are made up of only eight elements

Mineral Groups

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Silica and oxygen combine to form the basic building block for the silicates

The most common minerals

More than 800 silicate minerals

Make up 90% of the Earth’s crust

Mineral Groups

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The remaining mineral groups are often referred to as the nonsilicates

Far less abundant in Earth’s crust

Some are very important economic minerals

Mineral Groups

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The silicon-oxygen tetrahedron is the building block of all silicates

Four oxygen atoms covalently bond to a much smaller silicon atom

Tetrahedra can be joined into chains, sheets, or three-dimensional networks by sharing oxygen atoms

Silicate Minerals

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Silicate Minerals

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Feldspars are the most plentiful silicates

Over 50% of Earth’s crust

Quartz is second-most-abundant mineral in continental crust

Only common mineral composed completely of Si and O

Silicate minerals tend to cleave between the strong siliconoxygen structures

Silicate Minerals

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Most silicate minerals crystallize from molten rock as it cools

Environment and chemical composition determines which minerals are produced

Some silicate minerals form at Earth’s surface as other silicates are weathered

Some silicate minerals form at extreme pressures during mountain building

Silicate Minerals

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Common light silicate minerals include:

Feldspars

Quartz

Muscovite

Clay minerals

Contain varying amounts of aluminum, potassium, calcium, and sodium

Silicate Minerals

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Feldspars are the most abundant

Found in igneous, sedimentary, and metamorphic rocks

Have two directions of cleavage at 90º

6 on Mohs hardness scale

Potassium feldspar contains potassium ions

Plagioclase feldspar contains calcium and/or sodium ions, and has striated cleavage surfaces

Silicate Minerals

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Silicate Minerals

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Quartz is common in igneous, sedimentary, and metamorphic rocks

Impurities cause a variety of colors

7 on Mohs hardness scale

Forms hexagonal crystals with pyramid-shaped ends

Exhibits conchoidal fracture when broken

Silicate Minerals

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Silicate Minerals

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Muscovite is a member of the mica family

Excellent cleavage in one direction

2.5 on Mohs hardness scale

Clay minerals are commonly the weathering product of other silicates

Common part of soil

Nearly half of the volume of sedimentary rocks is clay minerals

Silicate Minerals

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Silicate Minerals

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Dark silicate minerals contain iron and magnesium

Pyroxenes

Amphiboles

Olivine

Biotite

Garnet

Dark color and high specific gravity from iron content

Silicate Minerals

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Olivine is a major constituent of dark igneous rocks

Abundant in Earth’s upper mantle

Black to olive green color, glassy luster, and granular

Pyroxenes are an important component of dark-colored igneous rocks

Augite is black and, opaque and has two directions of cleavage at nearly 90º

The amphibole group includes minerals that commonly make up the dark portion of light-colored rocks

Hornblende is a dark black mineral with two cleavage planes at 60º and 120º

Silicate Minerals

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Silicate Minerals

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Biotite is a dark, iron-rich member of the mica family

Excellent cleavage in one direction

Common in light-colored rocks

Garnet is a dark silicate

Glassy luster, no cleavage, conchoidal fracture

Color varies, but commonly deep red

Well-developed crystals have 12 diamond-shaped faces

Most commonly found in metamorphic rocks

Silicate Minerals

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Silicate Minerals

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Nonsilicate minerals are divided into groups based on the negatively charged ion common to the group

Nonsilicates make up only about 8% of Earth’s crust

Some occur in significant amounts in sedimentary rocks

Some are economically important

Nonsilicate Minerals

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Nonsilicate Minerals

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Carbonates contain a carbonate ion

CO32

Calcite and dolomite

Used as road aggregate, building stone, and cement

Halite and gypsum are common evaporites

Halite (a halide) is table salt

Gypsum (a sulfate) is used in plaster

Oxides are important iron ores

Nonsilicate Minerals

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Other economically important nonsilicate minerals include:

Sulfides (galena, sphalerite)

Native elements (gold, silver, copper)

Fluorite

Corundum (ruby, sapphire)

Uraninite

Nonsilicate Minerals

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