In order to complete this EarthCache lesson, you will need to bring a magnifying glass with you. For this reason, this EarthCache's difficulty rating is a bit higher.
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Most of the world's beaches are made of quartz-rich sand. This is true for most of the world's continents because the sands are derived from the weathering and erosion of the land masses and their mountains. The land masses and mountains are composed of rocks that are in turn themselves composed of many common minerals, such as quartz, feldspar, amphiboles, and mica, for example. During the weathering process ground waters and dissolved carbon dioxide react with the rocks to break them down. Quartz has the particular ability to survive because it is very stable (unreactive to weathering processes) and because it is very hard - relative hardness is measured from one to ten on the "Mohs Scale", with Talc = 1, Gypsum = 2 (as hard as a finger nail), Calcite = 3, Fluorite = 4, Apatite = 5 (as hard as a knife blade), Feldspar = 6, Quartz = 7, Topaz = 8, Corundum = 9, and Diamond = 10. During weathering, feldspar (an aluminosilicate) rather rapidly converts to clays, while quartz, being unreactive silicon dioxide, survives the weathering process and eventually makes its way to accumulate along the beaches. The clays that were formed by the alteration of the feldspars are winnowed out from the surf zone and washed away to the open ocean to accumulate on the continental shelf and beyond. The quartz remains behind, traveling down the coast line (because the waves approach the coast line obliquely) as a narrow ribbon of sand in what's called longshore or littoral drift. (In reality, the beaches of the continents are actually different mixtures of quartz, feldspars and rock fragments, but quartz is usually dominant).
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The 26-miles of sand beach in Harrison County, Mississippi, is the longest (and largest) man-made beach in the world.
The Mississippi Gulf Coast's most famous beach is completely man-made...sort of. According to the Army Corps of Engineers, since the 1950s more than 30 million cubic yards of sand (originating from 1,500 feet out in the Mississippi Sound) has been deposited on the beach (over 6 million cubic yards of sand were used to create the original beach when it was first made in the early 1950s). So while the beach is technically "man-made", the sand that you are standing on is quite real!
A popular misconception among tourists and even many locals is that the sand is bleached by the sun. This sand, in the truest sense of the word, is not sand at all but Appalachian Quartz that filtered it's way down to the coast from the Appalachian mountains after the last ice age, when the glaciers melted. That sand dune you are looking at today was perhaps once, thousands of years ago, a mountain top near the Georgia-South Carolina border.
Sediment reaching the Gulf along the Florida Panhandle, Alabama, and Mississippi coasts is almost entirely from erosion of hard rocks in the southern Appalachian Mountains. Quartz, a hard, durable mineral, survives transport by fast-moving streams, while softer minerals break down and dissolve, or remain suspended in the water. Sedimentary particles available for deposition along the northeastern Gulf Coast are thus pure white quartz.
Fast moving streams bring mostly grains of clear white quartz the short distance across the coastal plain to the Gulf of Mexico where it was moved by powerful longshore currents westward. These currents gradually deposited the quartz on thin ridges of sediment on the shallow sea floor leaving the white crystals to pile up and eventually form our beautiful beaches and barrier islands.
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In order to complete this EarthCache, you must send me the answers to the following questions and post a photo with your log (required):
1. Using your magnifying glass, take a close look at a small amount of the sand you have collected from the beach here (try to get the sand from an area that hasn't been disturbed for the best results). While the beach sparkles in the sun, and looks white to really light tan, you may be quite surprised by what you see under the magnifying glass. What color are the majority of the sand particles here as seen under the magnifying glass?
2. Do you see any other colors of sand particles under the magnifying glass? If so, what do you think they are made out of?
3. Why do you think the sand appears white/tan, but the individual sand particles are a completely different color?
4. Do the individual sand particles look smooth or jagged? Why do you think this is the case here?
5. Take a photo of yourself, your group, or something that identifies you and post it with your log (your face need not be in it).
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Sources:
Roadside Geology of Mississippi, Stan Galicki and Darrel Schmitz, 2016
The Geology of Mississippi, David Dockery and David Thompson, 2016
Harrison County Sand Beach Master Plan, 2007
