Geol 108 Lab #5 Rocks, Weathering, Minerals Week of October 1-5, 2012 Part I. Weathering of rock Granite Rock (an igneous rock) Rocks are composed of minerals. A mineral is a naturally occurring, inorganic, solid substance that has (1) a characteristic chemical composition; (2) an ordered internal structure that leads to (3) characteristic physical properties. As shown in Figure 1, the common rock granite is composed of several minerals. The minerals quartz, hornblende, and feldspar are easily identified in the rock. Examine the granite display. Then answer the following questions: ! Briefly describe what you observe in the three trays of granite. Include how the three trays (three samples) differ from one another.

Color Figure 1. Most rocks are aggregates of several kinds of minerals. From: Earth, 8th ed., Tarbuck & Lutgens, 2005.

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Fresh granite Weathered granite Very weathered granite

Part II. Clays Introduction to Clay

Clays and clay minerals have been mined since the Stone Age; today they are among the most important minerals used by manufacturing and environmental industries.

The term "clay" is applied both to materials having a particle size of less than 2 micrometers (25,400 micrometers = 1 inch) and to the family of minerals that has similar chemical compositions and common crystal structural characteristics. Clay and Water Water molecules are strongly attracted to clay mineral surfaces. When a little clay is added to water, a slurry forms because the clay distributes itself evenly throughout the water. This property of clay is used by the paint industry to disperse pigment (color) evenly throughout a paint. Without clay to act as a carrier, it would be difficult to evenly mix the paint base and color pigment. A mixture of a lot of clay and a little water results in a mud that can be shaped and dried to form a relatively rigid solid. This property is used by potters and the ceramics industry to produce plates, cups, bowls, and pipes. Environmental industries use both these properties to produce homogeneous liners for containment of waste. Weathering

Weathering of rocks and soil is the primary way that clays and clay minerals form at the Earth's surface today. The weathering process involves physical disaggregation and chemical decomposition that change original minerals to clay minerals; weathering is uneven, and many stages of breakdown may be found in the same clay sample.

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Station A. The swelling clay - montmorillonite Look at the dry volcanic ash in the jar, and compare it to the jar of dry montmorillonite. Notice they are nearly the same color. But how are they different? Let’s do a simple experiment to find out. 1. Examine the sample of wet volcanic ash. Describe the feel of the ash.

(…recall LAHARS from the volcanic hazards lab. Once lahars settle into place they are very difficult to remove with hand tools. Heavy machines are needed.)

Take 1/4 teaspoon (1.25 ml) of montmorillonite clay. Put in the small beaker. Add 1/4 teaspoon of water three times to the clay in the small beaker (one portion of clay to 3 portions of water). Stir. 2. How much clay is there now that you have added water? Use the measuring

spoons provided. What happened to the montmorillonite clay? 3. Describe the feel of the wet montmorillonite clay – how is it different than the ash? 4. Examine the poster, “Main scarp of the Rancho Camulos landslide.” The Northridge Earthquake of January 1994 triggered numerous landslides. The Rancho Camulos landslide was the second largest. As the resident geologist, what advice could you give people who live in this neighborhood? Station B. Kaolinite Clay Kaolin – named after the white clay found near Kao Ling, China. Kaolin comes from decomposition of feldspar in soft, disintegrating granite, gneiss, and porphyritic rocks. History The term kaolin is derived from the Chinese word "Kau-ling", meaning high ridge, having reference to the locality from which the richest supplies were obtained. In Georgia, kaolin was first mined in Colonial days and shipped to England. The famous Wedgwood Pottery used

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considerable amounts of clay from the colonies until the English mines were opened. This ended the mining in Georgia for over a century. In 1876, mining here was resumed, and at present continues as the major mineral production of the state. Georgia produces about 72% of the total kaolin production of the United States. Uses It is of interest to note that of the some one and one-half million tons of kaolin produced annually in the United States, approximately 56% is used in the paper industry. In paper-making, kaolin is utilized as a pulp filler as well as for coating. Filling adds weight, opaqueness, and whiteness; coating gives high gloss. Some newspapers have a kaolin content of about 2%, while magazines with a relatively high gloss contain on the average of 30%. With the advent of high-speed coating equipment, the production of paper clays increased to the extent that it has nearly doubled in the past ten years. Experiment:

Take 1/4 teaspoon (1.25 ml) of kaolinte clay. Put in the small beaker. Add 1/4 teaspoon of water three times to the clay in the small beaker (one portion of clay to 3 portions of water). Stir. 5. Does the kaolinte clay react the same to water as the montmorillonite clay? Explain.

Station C. Illite (green) Clay Illite - first described for occurrences in the Maquoketa shale in Calhoun County, Illinois, 1937. The name was derived from its type location in Illinois. Manufacturing uses - Illitic clays are used for manufacturing structural clay products such as brick and tile. Illite may also be useful for storing certain types of radioactive wastes, because it is less subject to transformation by heat than are other common clays and because it is highly specific for the sorption of cesium. (From: http://www.answers.com/topic/illite) Cosmetic uses - Green illite clay is proposed to be efficient at drawing oils and toxins from the skin. It is also referred to as French Green Clay. It is used for detoxification and exfoliation of the skin. Experiment:

Take 1/4 teaspoon (1.25 ml) of illite clay. Put in the small beaker. Add 1/4 teaspoon of water three times to the clay in the small beaker (one portion of clay to 3 portions of water). Stir.

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6. Does the illite clay react the same to water as the montmorillonite clay? Explain. Clay questions: 7. Of the three clays - a. Which clay would be the preferred type for the ceramic industry and why? b. Which one might be used as a drilling mud (to keep drill holes open)? (consider expansion when the clay comes in contact with water) Note: This same clay is dangerous if found in tunnels or road cuts. Because of its expandable nature, it can lead to serious slope or wall failure. Part III. More about Minerals A. Introduction Minerals can be grouped according to chemical composition. Examples: quartz feldspar these are three examples of the silicate group of minerals mica pyrite this mineral is one example of the iron sulfide group of minerals halite these are three important rock forming, non-silicate minerals calcite gypsum Silicate minerals (such as quartz, feldspar, amphibole) are not very soluable, even in weak acids, due to the powerful bonds among the silicon and oxygen ions in the crystal structure. However, minerals such as halite and calcite, have relatively weak bonds, so they dissolve in even the weakest acids. This dissolution is commonplace because rainwater generally is slightly acidic. The mineral pyrite (an iron sulfide mineral) causes environmental problems in some mining areas.

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B. Getting to know minerals ! Examine the minerals samples provided in lab. Follow the instructions of your T.A. for learning these minerals, and use the tables on pages 7-9. Metal ores Galena Magnetite Pyrite

Non-metallic minerals Biotite mica Calcite Graphite Gypsum

Halite Potassium feldspar Quartz Sulfur

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Crime solving using earth materials…..

The Federal Bureau of Investigations (FBI) has collected and studied soil samples, minerals, and other Earth material for criminal investigations since 1935 and thousands of cases involving Earth materials are studied in the United States each year. Throughout the world soil is usually collected at crime scenes, is routinely studied at crime labs, and is often used as physical evidence during crime trials. There really is more to soil than what's under foot!

A crime had been committed in the foothills of the Rocky Mountains, near Denver, Colorado. One month later a burning vehicle was found at a dump in New Jersey. Soil samples were taken from the fender of the burning car and were studied by forensic geologists. Analyses of the soil samples showed there were four layers of soil that had built up under the burning car's fender. The outer, most recently deposited layer of soil was from the New Jersey dumpsite. The three inner layers of soil contained minerals from the Rocky Mountain Front area near Denver, Colorado. Forensic geologists obtained 360 soil samples from the Rocky Mountain Front area to compare them with those found under the fender of the burning car in New Jersey. Soil samples were also taken from the victim’s ranch. One of the three inner layers of soil under the suspect's car fender matched the soil sample forensic geologists obtained at the crime scene. The second inner layer of soil under the suspect's car fender matched the soil sample forensic geologists obtained at the victim's ranch. The first inner layer of soil did not match any of the 360 soil samples taken by the forensic geologists but was determined to have originated from the Denver area. The suspect was convicted and jailed based upon the results using soil sample comparisons.

Reference: http://www.forensicgeology.net/science.html --------------------------------------------------------------------------------------------------------------------------------

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LUSTER (metallic or nonmetallic)

HARDNESS CLEAVAGE COLOR/STREAK OTHER PROPERTIES

NAME SOME USES

Example: metallic

H=2.5 Yes Shiny silver color Dark gray streak

Feels heavy (high specific gravity)

GALENA Ore of lead for TV glass, auto batteries, paint

metallic

H = 6 Black color Dark gray streak

magnetic Ore of iron for steel, brass, bronze, tools, nails & bolts

metallic

H = 6 – 6.5 Forms cubes or octahedrons; looks like gold

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LUSTER (metallic or nonmetallic)

HARDNESS CLEAVAGE COLOR/STREAK OTHER PROPERTIES

NAME SOME USES

nonmetallic

H = 1.5-2.5 Bright yellow color Smells like rotten eggs

nonmetallic

H =3 Yes, in 3 directions

Colorless, white, or yellow

Breaks into rhombohedrons; effervesces in dilute HCl acid

Used to make antacid tablets, fertilizer; Ore of calcium

nonmetallic

H = 2.5 - 3 Yes, splits into thin sheets

Brown-black color

BIOTITE MICA

Used for fire-resistant tiles, rubber, paint

nonmetallic

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LUSTER (metallic or nonmetallic)

HARDNESS CLEAVAGE COLOR/STREAK OTHER PROPERTIES

NAME SOME USES

nonmetallic

nonmetallic

nonmetallic

nonmetallic

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