Monday, May 06, 2013

Geological State Symbols Across the US - #4 Arkansas

The next state up is Arkansas. Here are the stats:

                                                                                        Year Established
State Mineral: Quartz Crystal                                                  1967
State Rock: Bauxite                                                                  1967
State Gemstone: Diamond                                                       1967

State Mineral: Quartz Crystal 

Quartz is one of the most abundant minerals in the crust of the Earth and easily one of the simplest minerals. It's chemical composition is SiO2 (silicon dioxide) and is a 7 on the Mohs Hardness Scale. Not only is it stable on the Earth's surface, it's harness means that it hangs around for a long time. This is the reason that the vast majority of sand is composed of quartz.

Quartz can be found in many different colors from purple (amethyst), to grey (smokey quartz), to white (milky quartz) but Quartz Crystal is often referred to the clear variety that has a crystal habit (pictured right), although any color of quartz can occur in a crystal habit. Quartz does not have any cleavage, meaning that when it breaks it doesn't form along perfect surfaces. Instead the Quartz Crystals grow, often by hydrothermal waters that are rich in dissolved silicon dioxide. As the waters flow over the crystals the silicon dioxide is deposited on the surface of the crystal, kind of like a stalactite in a cave.

Arkansas is known for the town of Hot Springs which has these hydrothermally heated pools flowing to the surface. These hydrothermal waters have produced some of the finest varieties of Quartz Crystals on the planet. There are many "dig your own quartz crystal" mines located in the areas around Hot Springs in the Ouachita Mountains, which allow people to dig for these crystals themselves. The Ouachita Mountains was considered to be a mystical location by the Native Americans and the Quartz Crystals were believed to have a sacred and spiritual significance, which is a belief of many holistic practitioners today.

State Rock: Bauxite

Unlike quartz and diamond, bauxite is by far the least known of the three Arkansas state symbols. Bauxite well known for being the primary ore of aluminum, of which the majority of the aluminum in the world is from bauxite. The primary minerals of bauxite are gibbsite (Al(OH)3), boehmite (AlO(OH)), and diaspore (AlO(OH)). To extract the aluminum, the bauxite is crushed into a powder and the aluminum is leached out via several chemical procedures.

The obvious use of aluminum is as a metal, but it can also be used for abrasives (one of the byproducts of the leaching process has a hardness of 9), in cements, and as proppants (discussed below). Currently the United States is not even in the top ten for bauxite producers and it is only produced in a handful of localities in the United States (Arkansas, Georgia, and Alabama). But that was not always the case. In Arkansas bauxite first saw production in 1899, and increased in production until 1923 when Arkansas produced half of the world's supply at 500,000 tons that year. The peak of production was in 1943 when 6,000,000 long tons were produced but it has had a steady decline ever since. Currently the Arkansas bauxite is mined for production of proppants, which are high density spherical grains used by the oil and gas industry in fracking.

State Gemstone: Diamond

One of the most famous gemstones, the diamond also is one of the hardest minerals on earth (it is actually the third hardest after two extremely rare minerals called Wurtzite Boron Nitride and Lonsdaleite ( Made up entirely of carbon, like its cousin graphite (also made up entirely of carbon), the arrangement of the carbon atoms and the strength of the bonds are what give the two minerals completely different properties. Diamonds are most often found in structures called kimberlites or lamproites. Kimberlites are magmatic rocks that are formed deep within the Earth's surface. The high pressure converts the carbon into diamonds and the structures make their way to the surface as buoyant globs of rock. Due to being formed at such high pressure, diamonds are inherently unstable on the Earth's surface, however they degrade at such a slow rate that it isn't much of an issue to jewelry.

Several kimberlites/lamproites are known in Arkansas, with the largest being located in Crater of Diamonds State Park, where visitors are allowed to mine for diamonds and keep what they find. The largest diamond found in Arkansas is called "The Uncle Sam" which was 40.42 carats before it was cut and was discovered in 1924 (figured right).


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