Geologic materials that are characteristically rich in fluorine are organic clays and shales, carbonatites, phosphates, hydrothermal ores and silicic igneous rocks such as rhyolites, dacites and granites (Selinus et al, 2010). | Geologic materials that are characteristically rich in fluorine are organic clays and shales, carbonatites, phosphates, hydrothermal ores and silicic igneous rocks such as rhyolites, dacites and granites (Selinus et al, 2010). |