Chapter 3 Matter and Minerals

CHAPTER 3 MATTER AND

MINERALS

MINERALS: BUILDING BLOCKS OF ROCKS By definition a mineral is

Naturally occurringInorganic solidOrdered internal molecular structure

Definite chemical composition Rock

A solid aggregate of minerals

COMPOSITION OF MINERALS Elements

Basic building blocks of mineralsOver 100 are known (92 naturally occurring)

AtomsSmallest particles of matterRetains all the characteristics of an element

WHAT ARE THE MOST COMMON ELELMENTS ON EARTH? oxygen is the big dog in town - it accounts for

46.6% of the earth's crust by mass (and 94% of it by volume!).

silicon at 27.7% of the crust by mass, we come up with the astounding realization that nearly 75% of the earth's crust is composed of silicon and oxygen. Wow!

The other six (6) elements are: Aluminum . . . . . 8.1% Iron . . . . . . . 5.0% Calcium. . . . . . 3.6% Sodium . . . . . . 2.8% Potassiun. . . . . 2.6% Magnesium. . . . . 2.1%

MOST COMMON MINERALS ON EARTH

SILICATES Silicates Consists of a small silicon atom with a

+4 charge surrounded in tetrahedral fashion by four larger oxygen atoms each having a -2 charge.

Net charge on the anion group is -4. To satisfy this charge deficiency the SiO4 tetrahedra can either bond with cations (Fe, Mg, Ca, K, Na) or join with other SiO4 tetrahedra through oxygen sharing.

TETRAHEDRON

TOP 10 MOST COMMON MINERALS The Common Rock Forming Minerals

Feldspar (silicate) Quartz (silicate) Muscovite (silicate)

Ferromagnesians Olivine (silicate) Pyroxene (silicate) Amphibole (silicate) Biotite (silicate) Muscovite (silicate) Calcite (not a silicate)

COMPOSITION OF MINERALS Atomic structure

Central region called the nucleusConsists of protons (+ charges) and neutrons (- charges)

ElectronsNegatively charged particles that surround the nucleus

Located in discrete energy levels called shells or valences.

STRUCTURE OF AN ATOM

Figure 3.4 A

The maximum number of electrons that an atom can have in it’s valence shell is 8 it is not balanced until it has eight in it’s outer shell.

The number of electrons in its valence shell corresponds to its group on the periodic chart.

Things to remember from chemistry:

1. The nucleus of an atom is composed of _________ and __________

2. The atomic number is the same as the number of __________

3. A chemical element is defined by its number of __________

4. Atomic Mass is the mass of the ______ and _____ of an atom.

COMPOSITION OF MINERALS

Chemical or Covalent bondingFormation of a compound by combining two or more elements in other words the electrons are_______.

Ionic bondingAtoms gain or lose outermost or ________electrons to form ions

Ionic compounds consist of an orderly arrangement of oppositely charged ions called ________

HALITE (NACL) – AN EXAMPLE OF IONIC

BONDING

Figure 3.6

ANOTHER NAME FOR HALITE IS ________ It has an ionic bond As we know this bond

is not strong since we can easily dissolve it in water.


Covalent bondingAtoms share electrons to achieve electrical neutrality

Generally ________than ionic bonds

Both ionic and covalent bonds typically occur in the same compound

COVALENT BONDING

Figure 3.7


Other types of bondingMetallic bonding

Valence electrons are free to migrate among atoms

Weaker and less common than other bonds

ISOTOPES : COMPOSITION OF MINERALS

Isotopes and radioactive decayMass number = sum of neutrons + protons in an atom

_________= atom that exhibits variation in its mass number

Unstable _________emit particles and energy in a process known as radioactive decay

STRUCTURE OF MINERALS

Minerals consist of an orderly array of _________chemically bonded to form a particular crystalline structure (meaning orderly)

Internal atomic arrangement in ionic compounds is determined by ionic size

GEOMETRIC PACKING OF VARIOUS IONS

Figure 3.8

STRUCTURE OF MINERALS

PolymorphsMinerals with the same composition but different crystalline structures

Examples include diamond and graphite

Phase change = one polymorph changing into another

DIAMOND AND GRAPHITE – POLYMORPHS OF CARBON

Figure 3.10

PART 2 PHYSICAL PROPERTIES

OF MINERALS

Primary diagnostic propertiesDetermined by observation or performing a simple test

Several physical properties are used to identify hand samples of minerals

PHYSICAL PROPERTIES OF MINERALS

Crystal formExternal expression of a mineral’s internal structure

Often interrupted due to competition for space and rapid loss of heat

A GARNET CRYSTAL

CUBIC CRYSTALS OF PYRITE

Figure 3.11 A


__________Appearance of a mineral in reflected light

Two basic categories____________________

Other descriptive terms include vitreous (glassy), silky, or earthy

GALENA (PBS) DISPLAYS METALLIC LUSTER


ColorGenerally unreliable for mineral identification

Often highly variable due to slight changes in mineral chemistry

Exotic colorations of certain minerals produce gemstones

QUARTZ (SIO2) EXHIBITS A VARIETY OF COLORS

Figure 3.26


_________Color of a mineral in its powdered form

_________Resistance of a mineral to abrasion or scratching

All minerals are compared to a standard scale called the Mohs scale of hardness

STREAK IS OBTAINED ON AN UNGLAZED PORCELAIN

PLATE

Figure 3.12

Mohs scale of

hardnessFigure 3.13


CleavageTendency to break along planes of weak bonding

Produces flat, shiny surfacesDescribed by resulting geometric shapesNumber of planesAngles between adjacent planes

PHYSICAL PROPERTIES OF MINERALS CONTINUED Cleavage is described in terms of how easy

the cleavage is produced. From easiest to hardest to produce the terms are:

perfect, imperfect, good, distinct, indistinct, and poor

Common cleavagedirection

sFigure 3.15

FLUORITE, HALITE, AND CALCITE ALL EXHIBIT PERFECT CLEAVAGE


_________Absence of cleavage when a mineral is broken

_________Weight of a mineral / weight of an equal volume of water

Average value = 2.7

CONCHOIDAL FRACTURE

Figure 3.16


Other propertiesMagnetismReaction to hydrochloric acidMalleabilityDouble refractionTasteSmellElasticity

MINERAL GROUPS Nearly 4000 minerals have been named Rock-forming minerals

Common minerals that make up most of the rocks of Earth’s crust

Only a few dozen membersComposed mainly of the 8 elements that make up over 98% of the continental crust

ELEMENTAL ABUNDANCES IN CONTINENTAL CRUST

Figure 3.18

MINERAL GROUPS Silicates

Most important mineral groupComprise most rock-forming minerals

Very abundant due to large % of silicon and oxygen in Earth’s crust

Silicon-oxygen tetrahedronFundamental building blockFour oxygen ions surrounding a much smaller silicon ion

Two illustrations

of theSi–O

tetrahedronFigure 3.19

MINERAL GROUPS Joining silicate structures

• Single tetrahedra are linked together to form various structures including

Isolated tetrahedraRing structuresSingle and double chain structuresSheet or layered structuresComplex 3-dimensional structures

THREE TYPES OF SILICATE STRUCTURES

Figure 3.21

MINERAL GROUPS Common silicate minerals

Light silicates: Feldspar groupMost common mineral groupExhibit two directions of perfect cleavage at 90 degrees

Orthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar) are the two most common members

POTASSIUM FELDSPAR

Figure 3.24

PLAGIOCLASE FELDSPAR

Figure 3.25


Light silicates: QuartzOnly common silicate composed entirely of oxygen and silicon

Hard and resistant to weatheringConchoidal fractureOften forms hexagonal crystals


Light silicates: MuscoviteCommon member of the mica family

Excellent cleavage in one directionProduces the “glimmering” brilliance often seen in beach sand


Light silicates: Clay mineralsClay 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


Dark silicates: Olivine groupHigh temperature Fe-Mg silicatesIndividual tetrahedra linked together by iron and magnesium ions

Forms small, rounded crystals with no cleavage


Dark silicates: Pyroxene groupSingle chain structures involving iron and magnesium

Two distinctive cleavages at nearly 90 degrees

Augite is the most common mineral in the pyroxene group


Dark silicates: Amphibole groupDouble 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

HORNBLENDE AMPHIBOLE

Figure 3.27

CLEAVAGE ANGLES FOR AUGITE AND HORNBLENDE

Figure 3.28

MINERAL GROUPS Important nonsilicate minerals

Typically divided into classes based on anions

Comprise only 8% of Earth’s crust

Often occur as constituents in sedimentary rocks

Table 3.2


CarbonatesPrimary constituents in limestone and dolostone

Calcite (CaCO3) and dolomite CaMg(CO3)2 are the two most important carbonate minerals


Many nonsilicate minerals have economic value

ExamplesHematite (oxide mined for iron ore)

Halite (halide mined for salt)Sphalerite (sulfide mined for zinc ore)

Native copper (native element mined for copper)

NATIVE COPPER

END OF CHAPTER 3

Chapter 3 Matter and Minerals

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