scibri (2544842) writes "Chemists have proved that a smelly rock is the only known place on Earth where fluorine exists in its elemental form, F2 (Abstract).
The rock is antozonite, a calcium fluoride (fluorite) mineral that is dark violet or even black in colour, also known as fetid fluorite or stinkspar. Needless to say, this rock stinks. The pungent smell is given off when antozonite is crushed, and chemists and mineralogists have argued over the origin of the stench since the early nineteenth century.
It turns out French chemist Henri Moissan, who first isolated fluorine in 1886, was right. The rock contains pockets of fluorine that are released on crushing."
Link to Original Source