Rocks and Minerals on Earth’s surface By Doba D. Jackson, Ph.D. Associate Professor of Chemistry...

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

– 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 Limestone Conglomerate

Slate GneissQuartzite

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 non-metal (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

MetalsNonmetals

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

BasaltAndesite

Diorite

Granite

Rhyolite

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/cm3Form- PlutonicMagma- 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 water-cooled 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.