CHALK. When you write on the blackboard with a piece of chalk, you hold in your hand the mineral remains (shells) of thousands of tiny creatures called foraminifera, which died millions of years ago. They lived in the seas, and as they died their tiny shells sank to the bottom and became consolidated into the soft limestone known as chalk. After long periods of time these beds were elevated and became parts of the dry land. This process of making chalk is still going on in warm ocean waters and perhaps some day earth disturbances will raise these deposits for the use of future generations.
It has teen estimated that it takes more than a million of these shells to form a cubic inch of chalk, but the number of these minute creatures was so incredibly large that great chalk deposits are found in many parts of the world. In the United States deposits occur in Texas, Kansas, and some other states of the great plains. Towering cliffs of chalk border the south coast of England, and great beds of it underlie large areas of England and France. In color chalk is usually white or whitish, and chemi cally it is chiefly carbonate of lime.
Chalk is largely used in cement making. When washed free from grit it is called whiting, and is used for making putty and as a polishing powder. Re fined chalk is also used in medicine. Mixed with some binding substance it becomes the crayons we use for marking. Colored crayons contain pigments also to give the desired color. In addition chalk is employed in making tooth powders, paints, and many chemical compounds. French chalk is not properly chalk at all, but a variety of talc (see Talc).