Chapter 1 Minerals: Building Blocks of Rocks. Minerals: Building Blocks of Rocks By definition a mineral is/has Naturally occurring Solid Ordered internal.

Chapter 1 Minerals: Building

Blocks of Rocks

Minerals: Building Blocks of Rocks

By definition a mineral is/has Naturally occurring Solid Ordered internal molecular structure Definite chemical composition Generally inorganic

Rock A solid aggregate of mineral, or

mineral like, matter that occurs naturally

01_03

Composition and Structure of Minerals

Elements Basic building blocks of minerals Over 100 are known (92 naturally occurring) most minerals are compounds (formed when

2 or more elements chemically combine) Atoms

Smallest particles of matter Retain all the characteristics of an element the atoms of elements combine to form

compounds

Composition and Structure

of Minerals Atomic structure

Central region called the nucleus Consists of protons (+ charges) and

neutrons (no charges) atomic number=number on protons,

this determines identity of the element

Electrons Negatively charged particles that

surround the nucleus Located in discrete energy levels (shells) determine chemical properties of

element

Structure of an Atom

Figure 1.5 A

01_05B


Chemical bonding Formation of a compound by

combining two or more elements Atoms gain (-) or lose (+) outermost

electrons to form ions, to satisfy octet rule. Oppositely charged ions attract one

another to produce a neutral chemical compound by forming ionic bonds

01_06


Isotopes and radioactive decay Mass number = sum of neutrons +

protons in an atom Isotope = atom that exhibits variation in

its mass number atomic weight(mass)=weighted av. of

mass numbers for isotopes of an element

Unstable nuclei of some isotopes emit particles and energy in a process known as radioactive decay

The precise rate of decay is useful for dating purposes (radiometric

dating)

Physical Properties of Minerals

Crystal form External expression of a mineral’s internal structure

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

Quartz

A Garnet Crystal

Cubic Crystalsof Pyrite

Figure 1.7 A


Luster Appearance of a mineral in reflected light

Basic categories Metallic-appearance of a metal Nonmetallic includes descriptive terms include

vitreous, silky, or earthy submetallic-appear slightly

metallic

Galena (PbS) Displays Metallic Luster

Figure 1.13


Color Generally unreliable for mineral identification

Often highly variable due to slight changes in mineral chemistry

Exotic colorations (due to impurities)of certain minerals produce gemstones

Inherent coloration is the true color of the mineral

Quartz (SiO2) Exhibits a Variety of Colors


Streak Color of a mineral in its powdered

form dark streak-metallic light streak- nonmetallic

Hardness 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 1.8

Mohs Scale of

HardnessFigure 1.9


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

01_17C

Fluorite, Halite, and Calcite All Exhibit Perfect

Cleavage

Figure 1.11


Fracture Absence of cleavage when a mineral is broken

Specific Gravity Weight of a mineral/weight of an equal volume of water

Average value = 2.5 – 3.0

Conchoidal Fracture

Figure 1.12


Other properties Magnetism Reaction to hydrochloric acid Malleability Double refraction Taste Smell Elasticity

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 members Composed mainly of the 8 elements that make up over 98% of the continental crust

Elemental Abundances in Continental Crust

Figure 1.14

Mineral Groups

Silicates-(dark and light) Most important mineral group

Comprise most rock-forming minerals

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

most crystallize from molten rock as it cools

Silicon-oxygen tetrahedron Fundamental building block Four oxygen ions surrounding a

much smaller silicon ion

Two Illustrationsof the Si–O

Tetrahedron

Figure 1.15

01_16

Mineral Groups

Common silicate minerals Feldspar group

Most common mineral group Quartz

Only common silicate composed entirely of oxygen and silicon

Potassium Feldspar

Figure 1.17

Quartz

Mineral Groups

Important nonsilicate minerals Comprise only 8% of Earth’s crust

Often occur as constituents in sedimentary rocks

Table 1.1

Mineral Groups

Important nonsilicate minerals Carbonates

Primary constituents in limestone and marble

Limestone is used commercially for road paving, building stone, and as the main ingredient in Portland cement

Mineral Groups Important nonsilicate minerals

A number of other minerals have economic value

Examples Hematite (oxide mined for iron ore) Sphalerite (sulfide mined for zinc

ore) Galena (lead) Native copper (native element

mined for copper)

Mineral Groups

Important nonsilicate minerals Halite and gypsum

Both are commonly found in thick layers

Like limestone, both halite and gypsum are important nonmetallic resources

Native Copper

End of Chapter 1

Chapter 1 Minerals: Building Blocks of Rocks. Minerals: Building Blocks of Rocks By definition a mineral is/has Naturally occurring Solid Ordered internal.

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