25 Mart 2013 Pazartesi

Missouri State Rock

Missouri State Rock


Mozarkite is a hard, lustrous, semi-precious variety of flint. As such, it is composed primarily of silica, SiO2. While the typical coloring of flint is a milky mix of browns and grays, mozarkite exhibits a wider range of hues including pinks, salmons and reds, blues and purples, and occasionally green. The colors form intricate designs that become especially clear when the stone is polished.
Missouri designated mozarkite its official state rock on July 21, 1967, at the suggestion of rock collectors from Kansas City and St. Louis. At the time, this distinctive local rock was responsible for drawing large numbers of rock collectors to the area and for the origins of the Lincoln Rock Swap.
Two early fanciers of the rock, Phillip Widel and Linville Harms, coined the name mozarkite in the 1950s. They formed the name from "mo" for Missouri and "zark" for the Ozark Mountains—Benton County, Missouri, the main source of mozarkite, is at the edge of the Ozark foothills. Before the coinage of this name, the rock was called "Missouri agate."
Flint most often forms as nodules in chalk, dolomite, or other limestone. The exact means by which the nodules form is uncertain. One theory suggests that empty spaces in the host rock fill with silica leached from the host rock. Another possibility is that the nodules form independently around the skeletons of marine organisms and are incorporated into the matrix stone as it forms. This explains why fossils as large as entire sea urchins are sometimes found in flint nodules. Flint can also fill in cracks and spaces between sediment layers in the host rock, and at other times it lies in massive deposits several meters thick.
Exposed flint surfaces, including the exteriors of flint nodules, develop a dull white coating or cortina that gives no hint of the lustrous interior. Thus, intact flint nodules may closely match the color of the rock in which they are found. Because of flint’s hardness, nodules protrude from eroded limestone and eventually wash free, winding up in streambeds and on seashores.
Mozarkite specifically is found in Benton County and a few other locations in southwestern Missouri. Colorful flint specimens are present in certain areas outside the state, such as the Alibates Flint Quarries National Monument in Texas and the Flint Ridge flint vein in Ohio, both important archeological sites. Flint is found on every continent.
It is hard to imagine the origins of human culture worldwide without flint. In numerous locations throughout the world, this rock was quarried by prehistoric people because of its usefulness in making sharp tools. Ancient flint quarries exist at Olduvai Gorge in Africa, regarded as the "cradle of mankind," and at Isampur in India, a site of early hominid settlement. 
Flintknapping, or chipping flint into shapes, was an essential prehistoric craft. Flint is an ideal rock for forming sharp tools because of the way it fractures. It does not contain lines of cleavage, so when struck, it breaks along the direction of the blow rather than following any internal structure.
Another prehistoric use of flint continued into the 19th century. Flint stones were struck against pyrite (FeS2) to make sparks to start fires, and later, against steel to ignite firearms.
Because of its hardness and its prevalence in some areas, flint was used at least since Roman times as a building material. Houses, walls, and churches of flint can be found in England and France.
State Rock
Slice of Mozarkite
State Rock
Mozarkite Sample
State Rock
A Jumble of Mozarkite
Name: Chalcedony
Chemical Formula: SiO2
Color: Occurs in every imaginable color

Author: World Trade Press

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