VIZUALIZING EARTH HISTORYBy Loren E. Babcock

Chapter 2

Earth Materials and Features

Rocks and MineralsDescribe the components of rocks.

Define and distinguish rocks, minerals, and crystals.

Rocks and minerals are the basic building blocks of the Earth. Both are key indicators of how Earth has developed through

time.

Rock – A rock is a mixture of minerals.

Mineral – A mineral is a naturally occurring crystalline solid or a synthetic, chemically identical equivalent.

Rocks and Minerals

Define biomineralization

Biomineralization – Biomineralization is the secretion of

minerals as bones, teeth, shells, external coverings,

or other structures by biological organisms.

Rocks and MineralsElements, ions, and atomic bonds

The basic building blocks of minerals are atoms of chemical elements.

Atoms - the smallest individual particles showing all the distinctive properties of a chemical element.

The nucleus is at the center of the atom. The nucleus contains most of the mass of the atom, protons

(positively charged particles) and neutrons (neutral particles).

Rocks and MineralsElements, ions, and atomic bondsFour types of chemical bonding

Ionic bond – In ionic bond one atom loses an electron from its outer shell to another atom.

Covalent bonding – In covalent bonding electrons are shared,

rather than exchanged between two atoms.

Metallic bonds – In metallic bonds atoms share clouds of electrons. Electrons in the outer shells drift from one atom to another as

a result of close packing of the atoms.

Van der Waals bonds – Van der Waals are a weak secondary attraction bonds between electrically neutral molecules

that have one positive end and one negative end.

Rocks and Minerals

Isotopes

The number of protons (positively charged particles)

in an atom are always the same, the number of neutrons

(neutral particles), however; could change giving an element

different isotopes.

The sum of protons and neutrons in the nucleus gives an

element its atomic mass (the weight of the electrons

surrounding the nucleus is very small).

Common Rock-Forming Minerals

Explain why the rock-forming minerals are important.

Minerals that make up rocks are divided into six

groups based on their chemical properties. About

20 rock-forming minerals are of primary importance

for interpreting Earth history.

The mineral groups that

contribute most to the rock record are the

silicates and the carbonates.

Common Rock-Forming MineralsSummarize the most important rock-forming minerals.

Silicate mineral – A silicate mineral has a silicate tetrahedron

(SiO4) as the basic chemical property. Silicates are the dominant group in igneous, sedimentary, and metamorphic rocks.

Carbonate mineral – These minerals have calcium, magnesium,

iron, or other ions attached to a carbonate ion (CO3-). They are

important sedimentary rocks, and can form the metamorphic rock marble.

Sulfate minerals – Sulfate minerals have calcium or other

ions attached to a sulfate ion (SO4-2). Most rock-forming

sulfate minerals, such as gypsum and anhydrite, occur in sedimentary rocks.

Common Rock-Forming MineralsSummarize the most important rock-forming minerals.

Halide minerals – Halide minerals have positive ions such as sodium and potassium attached to negative ions such as chlorine and bromine. Most rock-forming halides occur

in sedimentary rocks.

Oxide minerals - Oxide minerals have metallic ions combined with oxygen. Oxides occur in igneous,

sedimentary, and metamorphic rocks.

Sulfide minerals - Sulfide minerals have metallic ions combined with sulfur. They occur in igneous,

sedimentary, and metamorphic rocks.

The Rock Cycle

Rock cycle – The rock cycle is a conceptual model that describes the origin, alteration, and destruction of rocks

through the action of Earth processes.

The rock cycle, describes the processes by which rocks are formed, decomposed, transported,

modified, and formed again, is powered mostly by energy from the Earth’s internal heat and

from the Sun.

Cycles operate continuously, and have neither a beginning nor an end.

The Rock Cycle

The Rock Cycle

Igneous rocks

Magma - Molten rock, including any suspended crystals

(mineral grains) and dissolved gases.

Igneous rock – Igneous rocks are formed from

the cooling and crystallization of magma.

The Rock Cycle

Sedimentary rocks

Sedimentary rock — Sedimentary rocks are usually

layered, formed from sediments and minerals precipitated

under aqueous conditions.

Sediment — Sediments are unconsolidated particles of rock

that have been transported by agents of erosion and

unconsolidated particles formed as skeletal material

through biomineralization.

The Rock Cycle

Metamorphic rocks

Metamorphic rock — These are rocks whose original

mineralogy or texture has been transformed

through any combination of heat, pressure, chemical

environment (including hydrothermal fluids), or shearing stress.

Metamorphic rocks — result from the changing of rocks

through heat and pressure, which is commonly associated

with tectonic activity.

Types of Rocks

Differentiate between a descriptive classification

system and a genetic classification system of rocks.

Rocks can be classified in two ways:

1) a descriptive classification system - according to their

texture or fabric and their composition,

2) and a genetic classification system – classify rocks

according to their origin.

Types of Rocks

IGNEOUS ROCKS AND PROCESSES

Igneous rocks are formed through the cooling and

solidification of magma, are classified into two broad

groups based on their place of origin: intrusive (or plutonic)

and extrusive (or volcanic).

Types of Rocks

IGNEOUS ROCKS AND PROCESSES

Depending on their chemical composition igneous rocks

are classified in two main groups:

Light-colored (or felsic) igneous rocks

Dark-colored (mafic and ultramafic) igneous rocks

Types of Rocks

SEDIMENTARY ROCKS AND PROCESSES

Sedimentary rocks originate as unconsolidated particles

that undergo lithification, or a change to rock. Sedimentary

particles derive from three main sources:

1, fragments (clasts) produced by the weathering and erosion

of preexisting rocks;

2, skeletal debris produced by organisms; and

3, crystals precipitated from water, and commonly mediated

by the life activities of organisms.

Types of Rocks

SEDIMENTARY ROCKS AND PROCESSES

Lithification — Lithification involves the processes

involved in changing sediments to rock.

Sedimentary rocks are classified based on their composition.

Using this method, the principal categories of sedimentary rocks are siliciclastic rocks, carbonate rocks, and other rocks.

Types of Rocks

Sedimentary rocks

Two main steps are involved in changing loose,

unconsolidated sedimentary particles to solid rock:

1, deposition of sediments in layers; followed by

2, lithification (the processes responsible for

converting sediments to sedimentary rocks).

Types of Rocks

Sedimentary rocks

Deposition of sediments, layer by layer, is a key feature

of sedimentary strata— one of the primary distinguishing

characteristics of sedimentary rocks.

Sedimentary layering, which is also called bedding or

lamination, is visible at various scales ranging

upward from millimeter-scale layering.

Types of RocksSedimentary rock

Lithification involves compaction of sediments and cementation. The weight of the overlying sediment

causes layers below to become compacted, which results in a light shifting of the grains and reduction of many

pore spaces.

Cementation involves the precipitation of minerals out of water. As cementation proceeds, thin mineral deposits

grow on and between sediment grains, and those minerals both glue grains together and further reduce the

pore spaces between grains.

Types of Rocks

METAMORPHIC ROCKS AND PROCESSES

Metamorphic rocks form by the alteration of other

rocks at high temperatures and pressures. Metamorphism

causes chemical (mineralogical) and textural changes

in igneous, sedimentary, or other metamorphic

rocks.

Geologists describe metamorphism in terms of

grades (low, intermediate, and high) that reflect

temperature-pressure conditions during the time that rocks

are altered.

Types of Rocks

METAMORPHIC ROCKS AND PROCESSES

A common distinguishing characteristic of metamorphic

rocks is foliation.

Foliation is due to an alignment of crystals

that grow perpendicular to the direction of stress applied to

the rock during metamorphism.

Types of Rocks

METAMORPHIC ROCKS AND PROCESSES

Types of RocksMETAMORPHIC ROCKS AND PROCESSES

Low-grade metamorphism begins between 100˚C and 200˚C, and at about 1000 atm (atmospheres)

of pressure. Low-grade metamorphic rocks tend to be finely crystalline (fine-grained), and individual crystals usually need magnification to become visible.

High-grade metamorphism usually occurs above 500˚C and above 5000 atm of pressure. High-grade metamorphic rocks tend to be coarsely crystalline, and individual crystals are readily visible without

magnification. Foliation in coarsely crystalline rocks is often wavy or distorted.

Types of Rocks

METAMORPHIC ROCKS AND PROCESSES

Metamorphism of granitic rocks (granite and

rhyolite) also results in gneiss.

Metamorphism of basaltic rocks (basalt and gabbro)

results in greenschist (low-grade metamorphism);

amphibolite (intermediate grade of

metamorphism); and granulite

(high-grade metamorphism).

Types of RocksMETAMORPHIC ROCKS AND PROCESSES

Regional metamorphism is associated with the compressional stresses of mountain building and subduction zones.

Contact metamorphism occurs where hot granitic magma rises through preexisting rock (country rock) and releases heat

to the rocks it intrudes.

Burial metamorphism occurs in basins that subside under the great pressure of accumulating sedimentary layers.

Hydrothermal metamorphism occurs where hot waters pass through cracks in rocks, and may be associated with other areas where metamorphism of rock occurs.

Types of RocksMETAMORPHIC ROCKS AND PROCESSES