2. Examine the river sand in the figure and answer the following questions. Pame

Question

2. Examine the river sand in the figure and answer the following questions. Pamela Gore River sand, Atlanta, Georgia. (Scale in millimeters.) a. Using the guide in this lab (Figure 3.8), describe the sorting of this sand. Is this sand very well-sorted, well-sorted, moderately well-sorted, poorly sorted, or very poorly sorted? b. Using the guide in this lab (Figure 3.9), describe the roundness of this sand. Is this sand well-rounded, rounded, subrounded, subangular, or angular? c. Has this sand been in the depositional basin (river) for a long time or for a short time? d. This sand was derived from the weathering of granites and gneisses. What minerals do you expect to be in this sand, and why? e. Why is this sand brown? What has happened to it? f. Predict what will happen to this sand as it travels downstream to the Atlantic Ocean.

Explanation / Answer

a) Moderately well sorted

Explanation : The sand grains show a polymodal grain suze distribution with a wide variation in their sizes.

b) Subangular.

Explanation : The corners and edges of all the sand particles are not rounded. Most of them are angular while some are subrounded.

c) For a short time.

Explanation : The grain size distribution shows moderate sorting along with subangular grains. So it must have been collected from somewhere very near to it's source which has not suffered much transportation.

d) Expected minerals : Feldspars, pyroxene, amphibole, olivine, quartz, clay minerals.

These minerals constitute the rocks granite and gneiss and are resistant to the weathering processes. So, the weathering of these rocks will eventually result in the washing away of the unstable and less resistant minerals while the more resistant minerals are left behind as sediments.

e) The sand is brown in color due to its constituent mineral particles. It depends on the rocks from which the sand comes from.

f) As the sand travels down to the Atlantic ocean, due to greater and greater transportation, the sand grains will becone more rounded due to abrasion and the grains will become well sorted because the larger fractions will be removed eventually or they will decrease in size due to rounding by abrasion.

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