ARKANSAS ROCKS!!!! EarthCache
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Bauxite is not a mineral, but a rock with minerals in it. There are three kinds of rocks: Igneous, sedimentary and Metamorphic. Rocks are mined in many different ways depending on how close to the surface they are found.
The Arkansas bauxite region covers about 275 square miles in the northern part of the West Gulf Coastal Plain and is divided into two mining districts, Pulaski and Saline County
Bauxite takes its name from the village Les Baux de Provence in southern France, where geologist Pierre Berthier first identified it in 1821.
Bauxite is a sedimentary rock that is an aluminum ore. It is formed in weathered volcanic rocks. It costs a lot of money to get the aluminum out of other ores, so bauxite is important. Bauxite, the most common ore of aluminum, was designated the official state rock in 1967. It is a sedimentary material composed primarily of one or more aluminum hydroxide minerals, plus mixtures of silica, iron oxide, titania, aluminum silicates, and other impurities in minor or trace amounts.
Bauxite is the principal ore of aluminum and is a mixture of aluminum oxides and hydroxides that formed from intense chemical weathering of a soil in tropical environments. Soils formed under these conditions are termed laterites. In Arkansas, the aluminum-enriched soils are the result of the decomposition and lateritic weathering of nepheline syenite, an intrusive igneous rock. During the weathering process, leaching by rain, groundwater, and salt spray decomposed the original syenite minerals (feldspar and nepheline). Weathering removed much of the silica and concentrated the newly formed aluminum oxides and hydroxides as the rock termed bauxite. Geologically, the soils formed from syenite and weathered to laterites in the Paleocene Epoch (65–55 million years ago) along the west edge of a shallow marine basin that occupied the present Mississippi River Embayment in the central portion of the state. In the Eocene Epoch (55–34 million years ago), some of the bauxite deposits were stripped from where they originally formed and were deposited by freshwater streams in valleys and on the sides of topographically high areas in the Wilcox Group. Thus, there are two types of deposits recognized in Arkansas: in-situ (in place) and transported. Both have been economically important. In-situ deposits lie in blanket form on top of the original igneous rock, whereas transported bauxite deposits are generally smaller and resemble a wedge, with the earlier topography determining the base of the deposit. Transported bauxite contains cobblestones and boulders of bauxite set in fine-grained bauxite matrix.
Open pit mining is used to get bauxite in Arkansas. The water in bauxite is taken out of the ore. This leaves a white powder that is called alumina which is another name for aluminum oxide. Alumina is made into aluminum. The U.S. makes the most aluminum but doesn’t mine it here. We bring in the bauxite from other countries and use recycled aluminum to make things.
Bauxite is used in cement, chemicals, face makeup, soda cans, dishwashers, siding for houses, and other aluminum products. It is recycled so that it can be used over again. Bauxite is thought of as a rock because the minerals in it can be very different depending on where it is found. Actual minerals aren’t that changeable. Mineral identification is based on the‘sameness’ of the mineral each time a piece is found. For example, if you found a piece of halite, or salt, it would always look shiny or glassy, and always break evenly into cubes. Since the kinds of minerals that are in bauxite change a lot, it mineral identification changes from rock to rock, too. The‘sameness’ for mineral identification is not there so geologists think of it as a rock.
Rocks change over time depending on how much pressure, weathering, and erosion that they get. Pressure is the pushing down of top layers of rock on lower layers of rock.
Weathering is how the wind, rain, snow, etc. affect the rock. It’s what lots of rain storms do to it over a long, long time. Most of the time, weathering causes bits and pieces of rock to separate from larger chunks and washes them into streams and rivers. Erosion moves the pieces of rock from place to place using gravity, running water, or weathering. Erosion wears away rock over lots of time.
Rocks go through something called the rock cycle. This is where rocks change over a lot of time. Time, to a rock, is thousands and millions of years. A rock can begin as one kind of rock and then change many times before it is mined. Underground heat and the pressure we were talking about, plus weathering can change rocks over millions of years.
Rocks, minerals, and gemstones are mined in many different ways depending on how close to the surface they are found. In open pit mining, layers of dirt are taken off the top until they get down to the rock they want to mine.
Areas where bauxite was mined by open–cut methods after 1971 have to be reclaimed under Arkansas state law. This task involves moving millions of tons of waste rock material back into the large excavations created during mining. As the pits are being partially backfilled, the surrounding landscape is graded and shaped to provide drainage and eliminate high walls. At the conclusion of the needed earthwork, the top layer of the acid mine spoil is neutralized to create a new layer of soil for plant growth. The lands are then revegetated to prevent erosion. Reclaimed bauxite mines will be suitable for many different potential uses in the future.
To obtain credit for this earthcache, please answer the following
questions and send them to me before posting as a find or I will have to remove it until the answers are received as is required by geocaching rules:
1. What did you find at N34 33.333 W92 30.491? Please describe the
objects by size, color and number located here.
2. What type mining is used to get the bauxite located in Arkansas?
The Bauxite Museum is open Wednesday from 10:00 in the morning until 2:00 in the afternoon and on Sunday afternoon from 1:30pm to 4:00pm. Admission is free but donations are accepted.
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