What is "blue john"

Etymology 1 n. (context UK Derbyshire English) A semiprecious mineral, a form of fluorite with bands of a purple-blue or yellowish colour. Etymology 2

alt. (context US English) Completely skimmed milk, sometimes soured. n. (context US English) Completely skimmed milk, sometimes soured.

Blue John may refer to:

• Blue John, Kentucky
• Blue John (mineral), a form of fluorite mined in Derbyshire, England
• Blue John Cavern, a cavern in Castleton, Derbyshire where fluorite is mined
• Blue John 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

Blue John is an album by American organist John Patton recorded in 1963 but not released on the Blue Note label until 1986.

Blue John (also known as Derbyshire Spar) is a semi-precious mineral, a form of fluorite with bands of a purple-blue or yellowish colour. In the UK it is found only at Blue John Cavern and Treak Cliff Cavern at Castleton in Derbyshire. During the 19th century, it was mined for its ornamental value, and mining continues on a small scale. Deposits of fluorite have been recently found in China with colouring and banding similar to the classic Blue John stone.