ENVIRONMENTAL GEOLOGY IN THE NEWS

• Local
• Rocks for beneath your bird feeder.
• Neil Lane (NSF) on campus. Comment about the role of govt. in science and support of fundamental/applied science or how to live with shrinking budgets
• Regional
• Open pit copper mining in Wisconsin, Is it safe?
• What does drinking a glass of water from a water treatment plant prove?
• National
• Hurricane Fran - Direct hit on Cape Fear. Should we cover rebuilding, what does property mean when it is so transitory, who pays for rebuilding, should zoning laws be changes, is this a local, state, or federal government issue.

NaCl song and how real minerals are made up.

NET charge of crystal is zero, but no such thing as a "molecule" of NaCl in halite. Each Na surrounded by 6 Cl's and each Cl surrounded by 6 Na's that IN AGGREGATE form an electrically neutral crystal.

Crystal model - HALITE

What about the edges? Broken bonds give crystals surface a small charge that affects its ability to adsorb other ionic substances in solution. Sorption/desorption properties very important for movement of contaminants in the system.

Mineral classes and origins

• Minerals form in many diverse environments; deep in the earths crust and mantle, near the surface; on land, in lakes, in the ocean, from evaportion of water, solidification of melts, recrystallization under intense pressure and/or temperature, in response to weathering at the earthís surface.
• Many mineral species (several thousand), but only a relatively few make up the vast majority of all rocks on earth. Others generally minor to very rare, a feature that puts limits on their availability requiring exploration and development to find suitable reserves for industrialized society.
• By far the most abundant minerals are a class known as the silicates.
• Relatively few silicate minerals make up the vast majority of rocks.
• These silicates are classified depending on how the crystal structural arrangement of the silicon-oxygen bonds in the crystals

ROCKS

Rocks made of minerals, but how they are interlocked, which minerals make up the rock and in what proportion, and where the rock formed are all features that help us distinguish rocks from one another

Three Major Rock Types

1. IGNEOUS
2. METAMORPHIC
3. SEDIMENTARY

Major Textural Features of Rocks

Layering

Interlocking fabric of minerals (packed together with pore space, interlockng, equant or elongate)

Examples of major rock types within each major group

1. Igneous (Intrusive type/Extrusive type)
1. Granite/Rhholite/Obsidian
2. Gabbro/Basalt
3. Granodiorite/Andesite
2. Sedimentary
1. Shale
2. Siltstone
3. Sandstone
4. Conglomerate
5. Limestone
6. Evaporite (Halite, Gypsum rocks)
3. Metamorphic
1. Slate
2. Phyllite
3. Schist
4. Gneiss
5. Marble

Conditions of formation of the major rock types

1. From a melt
1. On surface (lava) - Volcanic, extrusive
2. Within the earth (magma) - intrusive
2. By compaction from minerals transported to sites of deposition (rivers, wind, glaciers, mass movement)
1. sand -> sandstone
2. silt -> siltstone
3. Clay -> shale
4. Gravel -> congolmerate
5. Lime mud and animal shells -> limestone
3. From a previous rock by burial, heating, or both
1. sandstone -> quartzite
2. Limestone -> marble
4. Shale -> slate -> schist -> gneiss -->(melting)->granitic (igneous)

The last process shows the link between sedimentary, metamorphic, and igneous rocks

ROCK PROPERTIES

• Strength
• Resistance to chemical and physical breakdown
• Ability to transmit fluids
• Porosity
• Permeability

THE ROCK CYCLE

Formalization of the relationship among rock types

Weathering (a process) reduces rock to sediment and dissolved matter. Sediment is transported via streams, glaciers, and wind to sites of deposition where it is buried and lithified into sandstone, shale, etc.

All types of rocks can be related to one another through processes that transform one type of rock to another.

Metamorphic rocks can be derived from igneous, sedimentary, and even other metamorphic rocks

Metamorphic rocks can be heated to such high temperatures (generally at high pressures as well) that they begin to melt and move upwards as less dense ìfluidsî that rise to higher levels within the crust to resolifify as either intrusive or extrusive rocks.

Sedimentary rocks can be formed from the breakdown of older igneous, metamorphic, and even sedimentary rocks through the processes of weathering, erosion, transportation, and deposition.

Generally these cycles take millions to tens or even hundreds of million years, but the important thing is that one type can be derived from another throughout its long geologic history.

Cycles are processes linking rock types.

DISTRIBUTION OF ROCKS ON EARTH

IGNEOUS

Basalt (and gabbro) the most abundant rock in the earthís outer shell (crust) and found mainly, but not exclusively in the oceans.

Granite and closely related rocks are most abundant on the continents and almost exclusively restricted to the continents.

SEDIMENTARY

Most old sedimentary (> 200 my) rocks are found on the continents.

Younger sedimentary rocks (<200 my) are found on the continents and in the oceans, but most are forming today in the oceans.

METAMORPHIC

Most old metamorphic rocks are found in old core areas of the continents (shields) and underlying the blanket of sedimentary rocks on the continents.

Metamorphic rocks are forming today in the cores of active mountain ranges, in the oceanic ridge system and at or near the base of the continents.

Note: In all cases no rocks older than approx 200 my are found in the oceans AT ALL! An important fact that underlies discussion that follows on PLATE TECTONICS

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