WEB EXERCISE - The Virtual Sand Collection http://faculty.pasadena.edu/dndouglas

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WEB EXERCISE - The Virtual Sand Collection

http://faculty.pasadena.edu/dndouglass/sand/SandPile/SanClem.htm

This light color sand appears tan to naked eye, but most of the grains are colorless under the microscope. The composition of this sand is similar to the composition of granitic rocks found in nearby mountains, namely minerals such as feldspar, quartz and biotite.

Sand #1 - California Beach Sand, San Clemente, California
http://faculty.pasadena.edu/dndouglass/sand/SandPile/SanClem.htm

1 - Describe how the colorless of the mineral breaks (describe the cleavage or fracture).

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2- Identify the colorless mineral. It is one of three minerals listed above.

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3- Look for the granite of biotite in the sand. Based on what you learned about mineral weathering in this lab, what two weathering processes affect biotite, and what are the weathering products of each (what new minerals are formed as biotite is weathering)?

Weathering process affecting biotite

Weathering product
(new mineral)

4 - Because biotite weathers easily, what does the presence of biotite in this sand suggest about how much these grains have been weathered and how far they have been transported. Which is the correct answer?

            a. Heavily weathered and/or transported far from the source area – or -
            b. Not weathered much and not transported far from the source area

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Sand # 2: Carbonate sand from Gun Beach, Guam

http://faculty.pasadena.edu/dndouglass/sand/SandPile/GunBech.htm

Sand # 3: Carbonate sand from O’Carrol’s Cove, Ireland.

http://faculty.pasadena.edu/dndouglass/sand/SandPile/Ocarrol.htm

Sand # 2 and # 3 are very different from those on California beaches. The sands are composed mainly of calcium carbonate produced by the activities of living organism. The sand consists of bits of shells, foraminifera tests, and pieces of other organism, such as algae or coral. Zoom in several times and examine the microscopic fossil in these two sands. These microfossils are called foraminifera (or forams for short), and their shells are called tests.

5- Sketch a foarm test form each sand as it appears under highest magnification:

Gun Beach, Guam

O’Carrol’s Cove, Ireland

6- The foraminifera are quite interesting, but they are very different in each sand. Why do you think the forams are so different? Hint locate Guam and Ireland on a map.

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7- Why do you suppose we don’t find carbonate sands dominated by foraminifera on beaches in Southern California? Hint: think about the source area lithology, climate and tectonic setting. How might one or all of these affect California sand to make it different from Sand # 2 and # 3?

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Weathering process affecting biotite

Weathering product
(new mineral)

Explanation / Answer

Sand #1 - California Beach Sand, San Clemente, California-

1) Concoidal fracture or breaking.

2) Quartze, Biotite, Plageoclase.

3) *Na feldspar and K feldspar undergo hydrolysis to form kaolinite (clay) and Na + and K + ions.

*The quartz (and muscovite if present) remain as residual minerals due to their high weathering resistance.
*Biotite and/or amphibole undergo hydrolysis to form clay, and oxidation to form iron oxides.
*Final product is Soil.

4) Not weathered much and not transported far from the source area, because Biotite is hydrogenous minerals.

Note - as per chegg policy answer of only 4 subparts possible in one time.

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