Fluoride Ion
Fluoride Ion is considered a trace element, fluoride is any combination of elements containing the fluorine atom in the -1 oxidation state (fluoride ion).  Due to its reactivity, fluorine is found in nature as fluorine compounds or fluorides.  Fluoride inhibits various enzyme systems, erythrocyte glycolysis and binds Ca++, causing anticoagulation and other toxic effects.  In addition, fluoride is a mitogen for osteoblasts and stimulates bone formation. (NCI)