Earth materials
Digi
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 siliconoxygen 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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