When pressed against rough surfaces, the mineral readily crumbles leaving a clear mark on the surface. A less commonly known use of chalk is as an ingredient in some toothpaste due to its mild abrasive properties. Use the button to select a material and get started. This website places cookies on your computer to improve your experience. By continuing to browse the site, you are agreeing to our use of cookies. It usually ranges in color from white to light gray to buff and forms from sediment deposited in a saltwater environment.
Composed mostly of the mineral calcite and formed mainly from the remains of floating microorganisms and algae, chalk deposits often contain fossils of marine animals of various sizes.
The Cretaceous -age Niobrara Chalk in western Kansas was deposited in a massive inland sea that ran north to south across west-central North America about 80 million years ago. Monument Rocks and Castle Rock , two sets of chalk spires that rise above the plain in Gove County, are composed of chalk formed from the enormous amount of ooze that settled on the floor of a Cretaceous sea floor. At a microscopic level, there can be a lot of space between the fossil particles that make up chalk.
Land underlain by chalk directly below the soil is often well drained. In these areas, water that infiltrates into the soil encounters the top of the chalk and easily flows into the chalk's pore spaces. It then flows downward to the water table and then follows the direction of groundwater flow to a stream or another body of surface water.
In some areas, people drill water wells into subsurface chalk layers for residential, commercial, and community water supplies. In areas where oil and natural gas form in the subsurface, the pore spaces of chalk can serve as a reservoir. Many oil and gas fields are located where subsurface chalk units serve as reservoirs.
It yields oil and natural gas from both conventional and continuous reservoirs. Small pieces of chalk have been used by students for over years for writing on small slates and large classroom panels known as "blackboards".
It is an inexpensive and erasable writing material and the most widely known use of chalk. Much of the early blackboard writing was done with pieces of natural chalk or natural gypsum.
Today pieces of natural chalk and natural gypsum have been replaced by sticks manufactured from natural chalk; sticks manufactured using other sources of calcium carbonate; or sticks manufactured using natural gypsum. Gypsum chalk is the softest and writes smoothest; however, it produces more dust than calcium carbonate chalk. Calcium carbonate chalk is harder, requires more pressure to produce wide marks, and makes less dust. It is sometimes marketed as "dustless chalk" but that description is not quite true.
Even though most chalk today is not made from mineral chalk, people still use the name "chalk" for this familiar writing material. Article by: Hobart M.
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