Kansas State Stone
Chalk in its usual form is a soft, porous, and friable (easily crumbling) form of limestone. Like all limestone, it is a sedimentary rock composed primarily of calcium carbonate and formed from shells of marine organisms. Although chalk may be tinged with color by impurities such as iron oxide, pure chalk is white.
REPRESENTATIVE OF THE STATE
Kansans sometimes call chalk the "unofficial state rock." Common in the west central part of the state, chalk creates some stunning formations such as Monument Rocks and Castle Rock, which together were designated the nation's first National Natural Landmark. The formations are part of what geologists call the Niobrara Chalk, an extensive, fossil-rich bedrock that surfaces in buttes where more weather-resistant portions of the chalk have been isolated. Chalk quarries in the state have sometimes produced exceptional hard chalk, which was once used as fence posts.
Chalk forms by accretion (accumulation) of tiny particles of shell and sometimes from chemically dissolved calcium carbonate originally from shells. The particles typically accrete in layers underwater, particularly in marine environments but also sometimes in fresh water. As layers are buried under layers, pressure accumulates, compacting the particles. But no matter how great the temperature and pressure, chalk doesn’t metamorphose into marble, as other limestone can. As noted in the "Uses" section below, chalk only rarely becomes hard and durable enough to use for buildings.
Being a sedimentary rock, chalk lies close to the earth’s surface. It occurs in various places in the world, but nowhere in as great quantity as in northern Europe, where vast deposits stretch from Russia to England. In the United States, chalk occurs mainly in Texas, Alabama, Nebraska, and, of course, Kansas.
Most know chalk as a drawing medium used by children and artists. Over the ages, chalk has had many other uses as well. The earliest use of chalk was as a white pigment in paint and a component of plaster. Ancient Egyptians used chalk in the primer under their paintings on rock or wood. Whitewash made with chalk was used for centuries by farmers for homes and barns and was still routinely used in the U.S. in the mid-20th century.
Those who are familiar with the usual uses of chalk may be surprised to learn that some chalk can actually be used as an architectural stone. The chalk used for building, however, is not found above ground. As early as ancient Roman times, it was known that chalk mined from deep underground was relatively hard and durable. The secret was to find chalk that had never been frozen, because freezing renders chalk friable. Rather than trusting that a given block was impervious to weather, masons left the material out in the elements for two years to test it. Much too costly for general applications, architectural-quality chalk was long reserved for building churches.
Chalk to mark surfaces such as chalkboards, fabric (tailor’s chalk), and playing fields has been largely replaced by other substances. Today, chalk is still used in toothpaste and cosmetics. Heated chalk oxidizes, forming calcium oxide, which is used as a component of cement and as a flux in purifying steel.
The white cliffs of Dover, England, are probably the most famous chalk formation. The Cerne Abbas Giant (or Rude Man) and the Uffington White Horse are two of the enormous outlines cut into the chalk bedrock of various hillsides in southern England. Other magnificent chalk sites are the White Rocks in Northern Ireland and the "Alabaster Coast" in Normandy, France.
Chemical Formula: (Ca,Fe,Mg,Mn,Zn,Co)CO3
Color: Occurs in all colors, sometimes even multicolored
|Author: World Trade Press|