By: Xanxin Wang, Ph.D.,
China University of Geosciences (Wuhan)
Visiting professor at the University of Waterloo (1998-1999)
The element fluorine, ranking thirteenth in abundance in the Earth's Crust, is used by higher life forms in the structure of bones and teeth. The importance of fluoride in forming human teeth and the role of fluoride intake from drinking water in controlling the characteristics of tooth structure was recognized during the 1930s. Fluoridation of drinking water since then has been a common practice in many countries.
A mineral consisting largely of calcium carbonate (CaCO3 ). Next to quartz, it is the most abundant of the Earth's minerals. Crystallizing in the hexagonal system, calcite is noted for its wide variety of crystalline forms.