|Fluorospar or Fluorite|
Fluorine gas is wretched stuff. Nothing can tear-out valence electrons like elemental fluorine can. Watch it corrode solid brick here: link There's another video link along the sidebar there of fluorine eating through a dead chicken. Fluorine was too hot to handle for WW I trench warfare, and even Fritz Haber had to settle for chlorine, the next lower (and less reactive) halogen. Fluorine is superlative in a number of other ways: Uberchemist Martyn Poliakoff explains here: link
[added: an updated video here: link]
The name came from the rock in which it was found, and that mineral, fluorspar, was so named because it helped molten metal flow, a property known since the Middle Ages. Calcium fluoride is still used in welding flux. Fluorospar also glows blue when heated, and that property gave us the term fluorescence.
Fluorine and its heavier halide brethren are the polar opposites of the alkaline earths: Li, Na, K, Cs, etc. Here's some raw video of two polar extremes going at it: link making salt (halogen means salt-forming in Greek) and a bunch of energy.
Hydrofluoric acid (HF) burns are particularly nasty: a decent amount of it burns right through flesh, overpowering the natural buffering system, and it keeps burning through flesh until it finds bone because calcium is the natural bonding partner of fluorine (as in fluorospar). I once witnessed the aftermath of a grad student who suffered an HF burn: he had to be med-evaced to Denver.
During WW II, uranium hexafluoride (or "hex" as it was so aptly nicknamed) became the vehicle of choice for the gaseous diffusion of uranium isotopes. Consider that nearly every single atom of U-235 that went into "Little Boy" was first borne aloft by six little fluoride wings (as volatile UF6) before the Enola Gay carried them aloft en mass for Hiroshima. Teflon (polytetrafluoroethylene) was used by chemists during WW II to enable the safe handling of UF6 during isotope separation.
UF6 was also of early interest to the Manhattan Project, as told to me by Jacob Bigeleisen: link
*The title is my homage to Ludwig Mond who in the words of Lord Kelvin "gave metal wings," referring to Mond's discovery of nickel tetracarbonyl, Ni(CO)4, a volatile compound so insidiously poisonous that it packs a double whammy if inhaled: it nickel plates your lungs while poisoning you with carbon monoxide.