Chalk



Chalk is a form of limestone that is often used for drawing. It is a soft, white, porous sedimentary rock and is composed of the mineral calcite. Calcite or calcium carbonate's molecular structure is CaCO 3. Calcite forms under deep marine conditions from the gradual accumulation of minute calcite plates that shed from coccolithophores which are organisms. - Chalk also refers to magnesium silicate and calcium sulfate. - Chalk has a greater resistance to weathering and slumping than usual clays - There are steep cliffs where chalk ridges meet the sea - Chalk is found in small amounts in toothpaste and serves as a mild abrasive. - Magnesium carbonate is what's applied to hands to prevent excess sweat and reduce slipping in sports such as gymnastics, rock climbing and weight-lifting.

The "Chalk Group" is a European stratigraphic unit deposited during the late Cretaceous Period. In Kent, England the famous White Cliffs of Dover are forms of depositions. The Champagne region of France is mostly underlain by chalk deposits. Some of the highest chalk cliffs in the world occur at Mons Klint in Denmark.
 * __Deposits__**

__**Uses**__ Chalk is used to make quicklime and slaked lime, mainly used as lime mortar in buildings. __Blackboard Chalk__: A substance used for drawing on rough surfaces. Composed of natural chalk and made from the mineral gypsum (calcium sulfate). __Sidewalk Chalk:__ Similar to blackboard chalk, except it is formed into larger sticks and often more colors. It is used to draw on sidewalk, streets, driveways. It is mainly for children, but some adult artist use it as well. __Agriculture Chalk__: Is used to raise the pH in soils with high acidity. Most common forms are calcium carbonate (CaCO 3 ) and calcium oxide (CaO). __Powdered Chalk__: Used for grass and tennis courts to mark boundaries. If the ball hits the line, a cloud of chalk or pigment dust can be seen. __Magnesium Carbonate__: Used for gymnasts, rock climbers, weight lifters, and for the game tug of war, because once applied it removes perspiration and reduce slipping. __Tailor's Chalk:__ A hard chalk used by tailors to make temporary markings on cloth. __Toothpaste__: Contains small amounts of chalk to serve as a mild abrasive. __Antacids:__ chalk is actually very similar to antacids like Tums. The CaCO3 works well to neutralize stomach acid and stop ulcers from forming.

Chalk used in school classrooms comes in slender sticks approximately .35 of an inch (nine millimeters) in diameter and 3.15 inches (80 millimeters) long. Lessons are often presented to entire classes on chalk-boards (or blackboards, as they were originally called) using sticks of chalk because this method has proven cheap and easy. As found in nature, chalk has been used for drawing since prehistoric times, when, according to archaeologists, it helped to create some of the earliest cave drawings. Later, artists of different countries and styles used chalk mainly for sketches, and some such drawings, protected with shellac or a similar substance, have survived. Chalk was first formed into sticks for the convenience of artists. The method was to grind natural chalk to a fine powder, then add water, clay as a binder, and various dry colors. The resultant putty was then rolled into cylinders and dried. Although impurities produce natural chalk in many colors, when artists made their own chalk they usually added pigments to render these colors more vivid. Carbon, for example, was used to enhance black, and ferric oxide (Fe 2 O 3 ) created a more vivid red.
 * __History__**

Chemical Formula for Chalk

How to make chalk: 1. Find a mold for your sidewalk chalk. Anything from a toilet tissue roll or small paper cup to fancy candy molds will work. 2. Mix together 1 cup of Plaster of Paris with 3/4 cup of water. 3. Add color to your mixture using powdered tempera paint. 4. Blend well and let stand for a few minutes. 5. Pour your mixture into the molds you chose. 6. Set aside and let dry completely. 7. Once dry you can remove your chalk from the mold. 8. Set it aside to dry for approximately 24 hours more. 9. Take your chalk outside and create fun masterpieces!

What You Need

 * A Mold
 * 1 cup Plaster of Paris
 * 3/4 cup Water
 * Medium Sized Bowl
 * Powedered Tempera Paint

Formation
Ninety million years ago the chalk downland of Northern Europe was ooze accumulating at the bottom of a great sea. Protozoans such as foraminifera lived on the marine debris that showered down from the upper layers of the ocean. Their shells were made of calcite extracted from the rich sea-water. As they died a deep layer gradually built up and eventually, through the weight of overlying sediments, became consolidated into rock. Later earth movements related to the formation of the Alps raised these former sea-floor deposits above sea level.