Environment

Rock Cycle and Mineral Resources

Lecture 10

The Earth Is a Dynamic Planet

´ Geology ´ Study of dynamic processes taking place on the earth’s surface

and in its interior

´ Three major concentric zones of the earth ´ Core (Inner and Outer)

´ Mantle, including the asthenosphere

´ Crust ´ Continental crust

´ Oceanic crust: 71% of crust

What Are Rocks?

´ Mineral ´ Naturally occurring chemical element or compound that exists

as a crystalline solid

´ Mineral resource ´ Concentration that we can extract and process into raw

materials

´ Nonrenewable

´ Rock ´ Solid combination of one or more minerals

Igneous Rocks

´ Igneous rocks ´ Igneous—“fiery inception”

´ Magma—molten rock beneath Earth’s surface

´ Lava—molten rock when it flows onto Earth’s surface

Slow Cooling - bigger minerals with distinct crystal structure

Fast cooling - very fine grained, not crystalline

Intrusive vs Extrusive Rocks

Examples of Intrusive Igneous Rocks

´ Diorite is a coarse-grained, intrusive igneous rock.

Granite is a coarse-grained, light colored, intrusive igneous rock.

Examples of Extrusive Igneous Rocks

Basalt is a fine-grained, dark-colored extrusive igneous rock.

Obsidian is a dark- colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.

Pumice is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. The vesicular texture is a result of gas trapped in the melt at the time of solidification.

Oceanic and Continental Crust

´ Oceanic Crust made up of Basalt (extrusive igneous rock)

´ Continental Crust made up of Granite (intrusive igneous rock)

´ Basalt is denser than granite

Sedimentary Rocks  Composed of cemented mineral

grains/rock fragments

´ Created by: ´ Weathering: breaking rocks into smaller

pieces

´ Erosion: removing grains from parent rock

´ Transportation: dispersed by gravity, wind, water, and ice

´ Deposition: settling out of the transporting fluid

´ Lithification: transforming into solid rock

Sedimentary Rocks

 Geologists define four classes of sedimentary rock. ´ Clastic: rock fragments (clasts) cemented together

´ Biochemical: cemented shells of organisms

´ Organic: carbon-rich remains of plants or other organisms

´ Chemical: minerals that crystallize from water

ChemicalClastic OrganicBiochemical

Clastic Sedimentary Rocks

 Clast size/grain size  Diameter of

fragments/grains  Range from very coarse to

very fine  Boulder, cobble, pebble,

sand, silt, and clay ´ Gravel: coarse-grained sediment

(cobble, pebble). ´ Mud: fine-grained (silt and clay) ´ As transport distance increases,

grain size decreases.

Examples of Clastic Sedimentary Rocks

Conglomerate – clasts are gravel sized or larger.

Sandstone – clasts are sand grain sized.

Shale -clasts are the size of clay grains.

Biochemical Sedimentary Rocks

 Biochemical limestone ´ Principle compound is CaCO3

´ Forms in warm, tropical, shallow, clear, O2-rich, marine water

´ Composed of shell debris from diverse community (corals, clams, oysters, snails, brachiopods, plankton, forams, cocolithophores)

Organic Sedimentary Rocks

 Made of organic carbon— the soft tissues of living things  Coal—altered remains of

fossil vegetation ´ Accumulates in lush,

tropical wetland settings

´ Requires deposition in the absence of oxygen

 Oil shale—shale with heat altered organic matter (Kerogen)

Chemical Sedimentary Rocks  Evaporites—from evaporated seawater

´ Evaporation causes minerals to precipitate. ´ Thick deposits are the result of large volumes of water evaporating. ´ Minerals include halite and gypsum.

 Travertine—precipitated from groundwater ´ Occurs when groundwater reaches the surface ´ CO2 expelled into the air; reduced ability to hold carbonate.

´ Evaporation can also cause CaCO3 to precipitate. ´ Example: thermal (hot) or cold water springs and cave settings

´ In cave settings, Travertine builds up complex growth forms speleothems

Metamorphic Rocks

 Metamorphic rock—solid-state alteration of a protolith ´ Meta = change

´ Morphe = form

 Rocks which were originally igneous or sedimentary and have been changed by heat and pressure

 Rearrange the crystal structure of the original rock

 Limestone becomes marble; sandstone becomes quartzite, shale becomes slate

Metamorphic Rocks  Protoliths undergo slow solid-state changes in:

´ Mineralogy

´ Texture

 Metamorphic changes are due to variations in: ´ Temperature

´ Pressure

´ Tectonic stresses (compression and shear)

´ Amount of reactive water (hydrothermal fluid)

Types of Metamorphic Rocks

 Two major subdivisions—foliated and nonfoliated

´ Foliated—have a throughgoing planar fabric ´ Subjected to differential stress ´ Have a significant component of platy minerals

´ Classified by composition, grain size, and foliation type

Foliation

 Foliation—Latin folium, for leaf ´ Parallel planar surfaces or

layers in metamorphic rock

´ Gives the rock a streaked or striped appearance

´ Foliated rocks often break along foliation planes

 Due to ´ Preferred inequant mineral

orientation, or

´ Compositional banding (dark and light layers)

Foliated Metamorphic Rock

Types of Metamorphic Rocks

 Nonfoliated—no planar fabric evident ´Minerals recrystallized without

compression or shear.

´Comprised of equant minerals only

´Classified by mineral composition

NonFoliated Metamorphic Rock

The Earth’s Rocks Are Recycled Slowly

 Rock cycle ´Rocks are recycled over millions of years ´Erosion, melting, and metamorphism ´Slowest of the earth’s cycle processes

The Earth Is a Dynamic Planet

Minerals

´ Naturally occurring ´ Solid ´ Formed geologically ´ Crystalline structure ´ Definite chemical ´ composition ´ Mostly inorganic

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Mineral Classes

 Oxides (O2-) ´ Metal cations (Fe2+, Fe3+,

Ti2+) bonded to oxygen. ´ Examples

´ Magnetite (Fe3O4)

´ Hematite (Fe2O3) ´ Rutile (TiO2)

 Halides (Cl- or F-) ´ Examples

´ Fluorite (CaF2)

´ Halite (NaCl)

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Mineral classes

 Carbonates (CO32-)

´ Examples

´ Calcite (CaCO3)

´ Dolomite (Ca, Mg[CO3]2)

 Native metals

´ Pure masses of a single metal

´ Examples

´ Copper (Cu)

´ Gold (Au)

Mineral Classes

 Sulfides (S–)

´ Metal cations bonded to a sulfide anion.

´ Examples

´ Pyrite (FeS2)

´ Galena (PbS)

 Sulfates (SO42-)

´ Metal cation bonded to a sulfate anionic group.

´ Many sulfates form by evaporation of seawater.

´ Examples

´ Gypsum (CaSO42H2O)

´ Anhydrite (CaSO4)

Mineral Classes

´ Oxygen and Silicon are the two most abundant elements in the crust.

 Silicates – Silica- 4 oxygen atoms surround a single silicon atom, forming (SiO4)4- Each oxygen atom covalently shares 1 electron with the silicon atom, jointly filling its outermost shell.

Mineral Resources

 Naturally occurring mineral deposit

´ Concentrated

´ Can be extracted and used

´ Some are a single element

´ - Cu, Au, diamonds

´ Most are compounds

´ - NaCl, CaSO4

´ Metallic or nonmetallic

´ High and low-grade ores

We Depend on a Variety of Nonrenewable Mineral Resources

 Ore ´Contains profitable concentration of

a mineral ´May be high-grade or low-grade

 Metallic mineral resources ´Aluminum ´Steel: a mixture of iron and other

elements ´Copper ´Gold ´Molybdenum

We Depend on a Variety of Nonrenewable Mineral Resources

´ Nonmetallic mineral resources ´Sand ´Gravel ´Limestone ´Phosphate

Life Cycle of a Mineral Resource

 Mineral resources go through life cycle ´ Mining

- Locate and extract ´ Conversion to products

- Purify useful mineral - Manufacture product

´ Disposal or recycling - Some minerals corrode away - Metals wear through friction - Some are pollutants - Metals commonly are recycled

Supplies of Nonrenewable Mineral Resources Can Be Economically Depleted

´ Reserves ´Identified deposits from which we can extract the

mineral profitably at current prices ´ Economic depletion

´Occurs when extraction costs more than remaining deposits are worth

´ Depletion time ´Time to use a certain portion (usually 80%) of reserves

at a given rate of use

Supplies of Nonrenewable Mineral Resources Can Be Economically Depleted

´ Options when a resource becomes economically depleted ´Recycle or reuse existing supplies ´Waste less ´Use less ´Find a substitute ´Do without

What Are The Environmental Effects of Using Nonrenewable Mineral Resources?

´ Extracting minerals from the earth’s crust and converting them into useful products: ´ Disturbs the land

´ Erodes soils

´ Produces large amounts of solid waste

´ Pollutes the air, water, and soil