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VIZUALIZING EARTH HISTORY
By Loren E. Babcock
Chapter 2
Earth Materials and Features
Rocks and Minerals
Describe 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 Minerals
Elements, 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 Minerals
Elements, ions, and atomic bonds
Four 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 Minerals
Summarize 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 Minerals
Summarize 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 Rocks
Sedimentary 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 Rocks
METAMORPHIC 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 Rocks
METAMORPHIC 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 Rocks
METAMORPHIC ROCKS AND PROCESSES