Blue John

Blue John or Bluejohn may refer to:
 * Blue John, Kentucky, United States
 * Blue John (mineral), a form of fluorite mined in Derbyshire, England
 * Blue John Cavern, a cavern in Castleton, Derbyshire where fluorite is mined
 * Bluejohn Canyon, a canyon in Utah, United States, site of the Aron Ralston accident
 * Blue John (album), an album by organist John Patton
 * Lance-Constable Bluejohn, a character in the Discworld series, a member of Ankh-Morpork City Watch
 * Blue John Gap, a fictional location in Arthur Conan Doyle's short story The Terror of Blue John Gap