chapter ii matter and minerals

7/31/2019 Chapter II Matter and Minerals

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Matter and Minerals(Chapter 2 in text)


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Minerals: Building blocks of rocksDefinition of a mineral:

Naturally occurring

Inorganic solid Ordered internal molecular structure

Definite chemical composition

Definition of a rock: A solid aggregate or mass of minerals


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Quartz - A Common Mineral


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Periodic Table of the Elements


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Composition of ElementsAtomic structure

Central region called the nucleus

Consists ofprotons (positive charges) andneutrons (neutral charges)

Electrons

Negatively charged particles that surround

the nucleus Located in discrete energy levels called shells

protons (positive charges) and neutron


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Idealized structure of an atom


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Composition of mineralsChemical bonding

Formation of acompound by

combining two ormore elements

Ionic bonding Atoms gain or lose

outermost (valence)electrons to form ions

Ionic compoundsconsist of an orderlyarrangement ofoppositely chargedions


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Halite (NaCl)- An Example of Ionic Bonding


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Composition of mineralsCovalent bonding

Atoms share

electrons toachieve electricalneutrality

Covalentcompounds are

generally strongerthan ionic bonds

Both ionic andcovalent bondstypically occur inthe same


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Covalent bondingsharing of

valence electrons


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Composition of minerals

Other types of bonding

Valence electrons are free to migrate among

atoms


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Composition of minerals

Isotopes and radioactive decay

Mass number is the sum of neutrons plus

protons in an atom

An isotope is an atom that exhibits

variation in its mass number

Some isotopes have unstable nuclei thatemit particles and energy in a process

known as radioactive decay


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Structure of minerals

Minerals consist of an orderly array of

atoms chemically bonded to form a

particular crystalline structure

For ionic compounds, the internal atomic

arrangement is primarily determined by

the size of ions involved


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Halite (NaCl)

(Packing Related to Cation and Anion Size)


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Structure of minerals

PolymorphsValence electrons are free

to migrate among atoms

Two or more minerals with the same

chemical composition but different

crystalline structures

Diamond and graphite are good examples

of polymorphs

The transformation of one polymorph to

another is called a phase change

Exam le: Peanut Butter in a Hi h


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Diamond and graphite

polymorphs of carbon


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Physical properties of minerals

Crystal Form

External expression of the orderly

internal arrangement of atoms

Crystal growth is often interrupted

because of competition for space and

rapid loss of heat Note this isnt cleavage!


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The mineral garnet often

exhibits good crystal form


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Luster

Appearance of a mineral in reflected light

Two basic categories

Metallic

Nonmetallic

Other terms are used to further describeluster such as vitreous (oily), silky, or

earthy (like dirt)


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Galena is a lead sulfide that

displays metallic luster


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Color

Generally an unreliable diagnostic

property to use for mineral identification

Often highly variable for a given mineral

due to slight changes in mineral chemistry

Exotic colorations of some minerals

produce gemstones

But we use it anyway :)


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Quartz (SiO2) exhibits a

variety of colors


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Streak

Color of a mineral in its powdered form

Helpful in distinguishing different forms

of the same mineral

Hardness

Resistance of a mineral to abrasion or

scratching All minerals are compared to a standard

scale called the Mohs scale of hardness


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Cleavage

Tendency to break along planes of weak

bonding

Produces flat, shiny surfaces

Described by resulting geometric shapes

Number of planes

Angles between adjacent planes


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Three examples of perfect cleavage

fluorite, halite, and calcite


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Micas have perfect cleavage

muscovite


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Fracture

Absence of cleavage when a mineral is

broken

Specific Gravity

Ratio of the weight of a mineral to the

weight of an equal volume of water

Average value is approximately 2.7

Simply hefting a mineral works too.


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Conchoidal fracture


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Other properties

Magnetism

Reaction to hydrochloric acid Malleability

Double refraction

Taste

Smell

Elasticity


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Classification of Minerals

Nearly 4000 minerals have beenidentified on Earth (most of which wedont really worry about).

Rock-forming minerals

Common minerals that make up most ofthe rocks of Earths crust

Only a few dozen members Composed mainly of the 8 elements that

make up 98% of the continental crust


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Silicates

Most important mineral group

Comprise most of the rock-forming minerals

Very abundant due to large amounts ofsilicon and oxygen in Earths crust

Basic building block is the silicon-oxygen

tetrahedron molecule

Four oxygen ions surrounding a much

smaller silicon ion


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Silica Tetrahedra (1 Si, 4 Os)


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Silicate structures

Single tetrahedra are linked together to

form various structures including

Isolated tetrahedra

Ring structures

Single and double chain structures

Sheet or layered structures Complex 3-dimensional structures


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Common Silicate minerals

Olivine

High temperature Fe-Mg silicate (typicalmantle mineral - formed 100s km in Earth

Individual tetrahedra linked together by iron

and magnesium ions

Forms small, rounded crystals with nocleavage


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Classification of MineralsCommon Silicate minerals

Pyroxene Group

Single chain structures involving iron and

magnesium

Two distinctive cleavages at nearly 90 degrees

Augite is the most common mineral in the

pyroxene group


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Classification of MineralsCommon Silicate minerals

Amphibole Group

Double chain structures involving a variety of

ions

Two perfect cleavages exhibiting angles of

124 and 56 degrees

Hornblende is the most common mineral in

the amphibole group


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Hornblende Crystal

Habit and Atomic

Structure


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Muscovite


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Feldspar Group

Most common mineral group 3-dimensional framework of tetrahedra

exhibit two directions of perfect cleavage at

90 degrees

Orthoclase (potassium feldspar) andPlagioclase (sodium and calcium feldspar) are

the two most common members


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Potassium feldspar


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Plagioclase feldspar


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Clay minerals

Clay is a general term used to describe a

variety of complex minerals

Clay minerals all have a sheet or layered

structure

Most originate as products of chemical

weathering


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Clay Minerals(at high magnification)


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Classification of MineralsImportant nonsilicate minerals

Several major groups exist including

Oxides Sulfides

Sulfates

Native Elements

Carbonates Halides

Phosphates


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Carbonates

Primary constituents in limestone and

dolostone

Calcite (calcium carbonate) and Dolomite

(calcium-magnesium carbonate) are the two

most important carbonate minerals


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Many nonsilicate minerals have economic

value Examples

Hematite (oxide mined for iron ore)

Halite (halide mined for salt)

Sphalerite (sulfide mined for zinc ore)

Native Copper (native element mined forcopper)


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Native Copper (End Minerals)


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End Minerals

chapter ii matter and minerals

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