Other minerals such as topaz contain fluorine. Fluorides, unlike other halides, are insoluble and do not occur in commercially favorable concentrations in saline waters.  Trace quantities of organofluorines of uncertain origin have been detected in volcanic eruptions and geothermal springs.  The existence of gaseous fluorine in crystals, suggested by the smell of crushed antozonite , is contentious;   a 2012 study reported the presence of % F
2 by weight in antozonite, attributing these inclusions to radiation from the presence of tiny amounts of uranium . 
Like most heat shrink tubing, FEP shrink tubing can be used for general purpose applications and repairs as well as more specific applications covered by the military specification. FEP Heat Shrink Tubing follows military specification M23053/11 for class 1 and class 2. Class 1 FEP Heat Shrink has a smaller shrink ratio of :1 when compared to Class 2 FEP Heat Shrink , with a shrink ratio of :1. Class 1 FEP shrink tubing has a heavy wall while Class 2 FEP shrink tubing has a medium wall.
Both classes of FEP shrink tubing are non-stick and can be used to cover pressure and temperature probes, due to the FEP heat shrink tubing's high operating temperature range. M23053/11 tubing also has see-through characteristics for viewing splices after installation.