- Country of manufactureUkraine
Chalk is used for the letter on big boards for the general review (for example, at schools) (the formed school chalk ok for 40% consists of chalk (a calcium carbonate) and for 60% from plaster (calcium sulfate). At a lack of calcium medical chalk can be registered as an additive to food. It should be noted that at x - ray researches of a digestive tract apply substance which is mistakenly taken sometimes for chalk. Actually it is a suspension of also insoluble barium sulfate in water.
The basis of a chemical composition of chalk is made by a calcium carbonate with a small amount of a carbonate of magnesium, but usually there is also not carbonate part, generally oxides of metals. In chalk usually there is an insignificant impurity of the smallest grains of quartz and microscopic pseudomorphoses of calcite on fossil marine organisms (to a radiolaria, etc. ). Quite often large fossils of the Cretaceous meet: belemnita, ammonites, etc.