Fluorspar is the trade name for the mineral fluorite, which is composed of calcium fluoride.
"The Economic Aspect of Geology" by C. K. Leith
Diamond, marble, and fluorite are examples.
"The Nature of Animal Light" by E. Newton Harvey
Many of these granites contain tourmaline, fluorite and monazite.
"Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 3" by Various
Built to bring three light wavelengths (red, green and blue) into focus at the same point and reduce chromatic aberration, using ED, HD or fluorite glass.