Chapter 3 Minerals andRocks

Figure 3.5c

A mineral is a naturally occurring crystalline solid, inorganic, with definite chemical composition and distinct properties

What is a Mineral?

• Fundamental building blocks of inorganic Earth

• Various uses for modern economic development

• Important clues for the history of Earth

• Knowledge of minerals and rocks as the first important step to finding and better managing Earth resources

• Important to our health, lifestyle, economy

Importance of Minerals

Figure 3.2

• All matter, including minerals and rocks, made of atoms

• Atom structure: Nucleus (proton and neutron) and surrounding electrons

• Atomic number: The unique number of protons in an element’s nucleus

• Atomic mass number: The sum of the number of protons and neutrons

• Ion: Charged atom particles, reactions between different types of atoms

• Isotopes: Atoms of the same element with varied number of neutrons

• Note: some isotopes partition into the environment and can be documented in rocks and minerals

Chemical bonding Ionic bonds Covalent bonds Metallic bonds van der Waals bond

Basic Chemistry Review (2)

• Color and streak

• Luster

• Crystal form

• Cleavage

• Hardness

• Special properties (taste, smell, feel, tenacity,reaction to acid, magnetism)

Mineral Diagnostic Properties

Figure 3.5

Rock-Forming Mineral Groups

Silicon Oxygen Tetrahedron

Figure 3.9

• Useful material

• A group of silicate minerals

• Fire-retardant property: brake linings, insulations

• Fibrous minerals: white asbestos (less harmful?), blue asbestos (hazardous)

• Removal of asbestos: depending upon the properties of the asbestos used and the context in which they are used

Case History: Asbestos

• Aggregated solids of minerals

• Three major types of rocks delineated by origin

• Fundamental links between rocks and environment (resources, sources for acid rain drainage, land subsidence, structure foundation failures, etc.)

• Rocks deform in response to geologic force/stress

Rocks

Figure 3.14

• Cooled, crystallized/solidified from magma

• Records of Earth’s thermal cooling history

• Intrusive rocks: Crystallized/solidified beneath Earth’s surface

• Extrusive rocks: Crystallized/solidified at or near Earth’s surface

• Classification: Based on texture and composition

Igneous Rocks

Why do rocks melt?

• 1. Geothermal gradient: temperature increases within the earth

• 2. Decompression melting: as warm solid material rises the volume of overlying rock decrases

• 3 Addition of water to magmas lowers melting temperature

• Dictated by the rates of magma cooling

• The rates of cooling slower beneath the surface,much faster near or at the surface

• The slower the magma cools, the coarser the mineral particles in igneous rocks

• Igneous rocks formed from two stages of cooling, having distinctive, different-sized particles

Igneous Rock Texture (1)

Figure 3.16b

Figure 3.16c

Figure 3.15

• Depending on the composition of magma

• Felsic/granitic: Silica rich, typically related to continental crust

• Intermediate/andesitic: Commonly associated with convergent boundaries along the rim of Pacific

• Mafic/basaltic: Silica poor, usually related to the oceanic crust

Igneous Rock Composition

• Phaneritic (intrusive)

• Porphyritic phaneritic (intrusive)

• Aphanitic

• Porphyritic aphanitic

• Vitreous/glassy

• Vesicular

• Pyroclastic

Igneous Rock Texture (2)

Composition

Texture Felsic Intermediate Mafic

Intrusive Granite Diorite Gabbro

Extrusive

Vesicular

Pyroclastic

Rhyolite

Obsidian

Pumice

Tuff

Andesite

Obsidian

Tuff

Basalt

Obsidian

Vesicular Basalt

Common Igneous Rocks

• Formed at the surface environment conditions

• About 75% of all rocks exposed at the surface are sedimentary

• Reveal conditions on earth over time: fossils, climate, landscapes

• Help Determine relative age

Sedimentary Rocks

Figure 3.16d

Figure 3.16e

• Compacted and cemented from detrital sediments

• Formation processes: Transportation, deposition, compaction, and cementation

• Fossil-fuel bearing rocks

• Classified based on particle size

• Shale: The most abundant clastic rocks

Clastic Sedimentary Rocks

• Precipitated from chemical solutions and/or accumulated chemical, biological matter

• Classified based on composition and texture

• Limestone:: The most abundant nonclastic sedimentary rocks

• Common texture: Crystalline, microcrystalline, skeletal, oolitic, massive

Nonclastic Sedimentary Rocks

• Stratification: Law of original horizontality, law of supposition

• Cross-bedding: Movement direction of ancient currents

• Fossil content: Environment setting (continental, marine, or transitional)

• Fine-grained clastic rocks and limestone in humid region: very weak rocks causing environmental problems

Sedimentary Structure and Environment

• Changed rocks from preexisting rocks under solid state: NO MELTING!

• Changes in mineralogy and rock textures but little change in overall composition

• Agents of change: Temp, pressure, and chemically active fluid

• EVIDENCE of Earth’s dynamic processes: Tectonic movement and igneous intrusion

Metamorphic Rocks

• Foliation: Preferred alignment of platy mineral particles Slaty, schistosity, gneissic banding Typically classified by texture: Slate, phyllite,

schist, gneiss

• Nonfoliation: Random arranged and interlocked mineral particles Fine-grained, coarse-grained Typically classified by composition: Marble,

quartzite

Metamorphic Rock Texture

Figure 3.13

Rock Cycle

• Inappropriate use for construction materials

• Fossil fuel exploration and extraction from rocks

• Reservoir rocks for fuels, groundwater, as well as contaminants

• Rock foliation and strength: Site stability for large facilities (nuclear power plants, dams, airports, etc.)

Rocks and Environment

Figure 3.31

Rock Structure& Strength

Figure 3.32

Figure 3.28bFailure ofSt. Francis Dam inCalifornia

Figure 3.29a

Figure 3.29b

Figure 3.Ba

Figure 3.Bb

Figure 3.Bc