Transcript Rocks - Huntingdon College

Rocks and Minerals
on Earth’s surface
By
Doba D. Jackson, Ph.D.
Associate Professor of Chemistry
& Biochemistry
Huntingdon College
Outline of Lecture 3
• Part I: Minerals and Rocks
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Structure of inorganic compounds
Silicates
Carbonates
Common Rocks
Mineral Activity
• Part II: The Igneous Rocks
– Types of Igneous Rocks
– Types of Magma
– Bowen’s Rock formation
Outline of Lecture 3
• Part III: Volcanoes and Volcanism
• Part II: Weathering, Erosion
Introduction to Chapter 3
• What is a mineral?
A mineral is
– Naturally
– Inorganic
– Crystalline solid
– Characteristic physical properties
– Specific chemical composition.
The Rock Cycle
• What is a rock?
– A rock is an aggregate of minerals.
Granite
Slate
Limestone
Quartzite
Conglomerate
Gneiss
The Rock Cycle
The Rock Cycle
• What are the characteristics of each of
the three major rock groups?
• Igneous rocks
result from the
crystallization of
magma or the
consolidation of
volcanic ejecta.
The Rock Cycle
• Sedimentary rocks are typically
deposited in layers formed by the:
– consolidation
of rock
fragments
– precipitation of
mineral matter
from solution
– compaction of
plant or animal
remains
The Rock Cycle
• Metamorphic Rocks- that result from the
alteration of other rocks;
– Metamorphic
rocks usually
form beneath
Earth’s surface,
by
• Heat
• Pressure
• Chemically active
fluids.
The Rock Cycle connects the internal and
external processes of the earth
Matter, Atoms, Elements, and
Bonding
• What are the atomic number and atomic
mass of an atom?
– The number of protons in an atom’s nucleus
determines its atomic number, whereas an
atom’s atomic mass number is the total number
of protons and neutrons in the nucleus.
Matter, Atoms, Elements, and
Bonding
• Chemical bonding
– Atoms are joined to
one another by forces
known as bonding.
– Atoms of different
elements which are
bonded to one another
form compounds.
Types of Chemical Bonds
• Ionic Bonds
– Ionic bonds form when ions with opposite
electrical charges attract one another
Types of Chemical Bonding
• Covalent Bonds
– Covalent bonds atoms share electrons.
Native Elements vs Minerals
By definition native
elements are made
up of only one
chemical element,
such as:
– Gold (Ag)
– Silver (Ag)
– Aluminum (Al)
– Copper (Cu)
– Diamond (pure C)
Elements of the Earth’s Crust
• Why are there so few common minerals?
– Even though there are 92 naturally occurring
elements, only 8 of them are very common in
Earth’s crust.
– Most common minerals are made up of oxygen,
silicon, and one or more other elements.
Definitions of Ionic and Covalent
Bonds
• Ionic bonds are a result of a combination of a
metal (electropositive element) and a nonmetal (electronegative element).
– In ionic bonds, atoms are attracted to each other by
opposite charges.
• Covalent bonds are a result of the combination
of two non-metals (two electronegative
elements).
– In covalent bonds, atoms are attracted to each other
by a shared pair of electrons.
Points to consider: Ionic
verses Covalent compounds
Point 1: Ionic compounds are
usually solids (when pure)
Point 2: Ionic compounds
have very high boiling and
melting points
Point 3: Covalent compounds
can be either solids, liquids
or gases
Point 4: Covalent compounds
have relatively lower boiling
and melting points
A chemical representation of a
covalent compound (ethanol)
Some Chemical Properties of
the Elements
Metals
Nonmetals
Mineral Groups categorized by
the non-metalic component
• Most of the more than 3,500 known minerals are
silicates.
Silicates are composed of
silicon and oxygen
• Silicates –
– composed of
the silica
tetrahedra
Structures of Silicates in the
crystalline rocks
Ferromagnesium
silicate
Non-Ferromagnesium
silicate
Types of Silicates
• Ferromagnesian silicates - made up of iron,
magnesium, or both combined with other
elements.
• Usually dark colored
Types of Silicates
Nonferromagnesian silicates - lack iron
and magnesium
• light colored
Carbonate rocks are
sedimentary rocks
• Carbonates
– All carbonate minerals have the
carbonate radical (CO³)-² as in
calcite (CaCO³) and dolomite
[CaMg(CO³)²].
– Carbonate minerals are found
mostly in the sedimentary rocks
limestone and dolostone.
– Carbonates are derived from the
shells and hard parts of marine
organisms or are precipitated
as seawater evaporates.
Mineral Identification must be
confirmed by specific tests
• Mineral composition and structure
produce unique physical properties.
– Color
– Hardness
– Cleavage pattern
– Crystal form
– Density
– M.P. (if applicable)
– Elemental analysis
– Diffraction
Rocks are a collection of many
minerals
The Origin of Minerals
• As molten rock material known as magma
(lava at the surface) cools, minerals begin to
crystallize and grow, thus determining the
composition of various igneous rocks.
The Rock Cycle
• What are the characteristics of each of
the three major rock groups?
• Igneous rocks
result from the
crystallization of
magma or the
consolidation of
volcanic ejecta.
Types of Igneous Rocks
All Igneous rocks fall into two categories based
on how they were formed:
• Volcanic (extrusive) Rocks- These Igneous rocks
come from volcanic eruptions. The rocks form
through cooling of lava flows or condensation of
volcanic ash. In this case, the cooling process is
fast over several days, weeks.
• Plutonic (intrusive) Rocks- These Igneous rocks
form underground beneath the earth’s surface.
In this case, the cooling is slow over millions of
years.
Volcanic Rock Formation
• Volcanic rocks come from two sources:
– Lava: Molten magma flowing along
the earth’s surface
– Pyroclastic materials: gases, dust,
smoke purged into the air and settles
on the ground around the surface of
a volcano
Introduction to Magmas
• Magmas are differentiated based on the
relative proportions of silica (SiO4), Iron (Fe),
and Magnesium (Mg).
– Felsic magma – silica rich (>65%)
– Intermediate magma- silica content (53-65%)
– Mafic – silica poor (45-53%)
– Ultra-Mafic- silica very poor (<45%)
• A single magma can, however, yield different
rock types.
The Properties and Behavior of
Magma and Lava
External analysis of Igneous rocks
• What does the term texture mean?
– Texture refers to the size, shape, and arrangement
of mineral grains composing a rock.
• Aphanitic, meaning very
fine-grained (usually
extensive origins)
• Phaneritic, meaning very
course-grained (usually
intensive origins)
Major Igneous Rocks
Common Igneous Rocks
Diorite
Rhyolite
Andesite
Granite
Diorite
Basalt
Gabbro
Common Igneous Rocks
• Peridotite is an ultramafic rock, meaning that it
contains more iron and magnesium than basalt
and gabbro which are mafic. Its composition is
close to that of the mantle.
Density- 3.5-5.7 g/cm3
Form- Plutonic
Magma- Ultramafic
%Silica- <45%
Minerals
- Olivine
- Pyroxene
- Plagioclase
Common Volcanic Rocks
Basalt- is the most abundant
-
rock of oceanic crust.
Plutonic form- Gabbro
Density- 3.0 g/cm3
Texture- rough (extensive)
Magma- Mafic
% Silica- 45-53%
Minerals:
-
Plagioclase
Olivine
Pyroxene
Horneblende
Basalt from a lava flow
Basalt from watercooled lava
Common Volcanic Rocks
Rhyolite- rock found in the
continental crust.
- Plutonic form- Granite
- Density- 2.7 g/cm3
- Texture- rough (extensive)
- Magma- felsic
- % Silica- >65%
- Minerals:
-
Plagioclase
Quartz
Biotite
Horneblende
Pink Rhyolite
Porphylitic Rhyolite
Common Volcanic Rocks
Andesite- rock found in the
continental crust.
- Plutonic form- Diorite
- Density- 2.7 g/cm3
- Texture- rough (extensive)
- Magma- intermediate
- % Silica- 53-65%
- Minerals:
- Plagioclase
- Pyroxene
- Horneblende
Pyropholitic Andesite
Andesite
Common Plutonic Rocks
Diorite- rock found in the
continental crust.
- Plutonic form- Andesite
- Density- 2.7 g/cm3
- Texture- fine (intensive)
- Magma- intermediate
- % Silica- 53-65%
- Minerals:
- Plagioclase
- Pyroxene
- Horneblende
Diorite
Diorite
Common Plutonic Rocks
Gabbro- is the most abundant
-
rock in mid oceanic ridges.
Volcanic form- Basalt
Density- 3.0 g/cm3
Texture- fine (intensive)
Magma- Mafic
% Silica- 45-53%
Minerals:
-
Plagioclase
Olivine
Pyroxene
Horneblende
Gabbro
Gabbro
Common Plutonic Rocks
Granite- common rock found
in the continental crust.
- Volcanic form- Rhyolite
- Density- 2.7 g/cm3
- Texture- fine (intensive)
- Magma- felsic
- % Silica- >65%
- Minerals:
-
Plagioclase
Quartz
Biotite
Horneblende
Granite Rocks
Mount Rushmore (Granite)
Introduction to Volcanoes
• Volcanism is the eruption of magma, and
associated gases at the surface.
• Some magma erupts explosively as
pyroclastic (fire-broken) rock and other
erupts as lava flows.
Volcanism and Volcanoes
• What gases do
volcanoes commonly
emit?
– Gases, primarily water vapor,
constitute only a small
weight-percent of magmas.
– Lesser amounts of carbon
dioxide, nitrogen, sulfur
dioxide, and hydrogen sulfide
– Very small amounts of
carbon monoxide, hydrogen,
and chlorine gas.
– Erupted sulfide and sulfur
dioxide can have widespread,
significant effects on climate.
What is a Volcano
A volcano is a hill or mountain that forms
around a vent, where lava, pyroclastic
materials and gases erupt. There are several
kinds of volcanoes.
Types of Volcanoes
• Cinder Cones are small volcanoes
• Shield volcanoes are long wide volcanoes
• Composite volcanoes are tall volcanoes
Distribution of Volcanoes
• Volcanoes are not randomly distributed, but
occur in well-defined zones or belts.
– 60% circum-Pacific
belt
– 20% Mediterranean
belt
– 20% are at or near
mid oceanic ridges
Volcanoes at Divergent
Boundaries are rare
• Volcanic activity at or near mid-oceanic
ridges is mainly submarine, but in a few
places such as Iceland, it occurs above
sea level. The volcanoes that form are
mostly mafic shield volcanoes.
Most volcanoes are at
convergent boundaries
• The volcanism in the circum-Pacific and
Mediterranean belts is the result of subduction
along convergent plate boundaries.
Some Volcanoes are not near
any plates (intraplate volcanism)
• The Hawaiian Islands formed as a series of
volcanoes originating from a stationary mantle
plume as the Pacific Plate moved over it.