Ref.: Rosenberg, P.E. (1988) Aluminum fluoride hydrates, volcanogenic salts from Mount Erebus, Antarctica. American Mineralogist: 73: 855-860.
http://tea.rice.edu/jroberts/12.13.1999.html (photos)
This type of volcanism, of phonolitic composition, is indeed unique for Erebus and the East African Rift Zone (Killimanjaro).