Reading through Westgarth Forster's 1821, “A Treatise on a Section of the Strata from Newcastle to Cross Fell”, I came across the following (on page 216): “Fluor spar occurs in veins in a great many different colours, viz. white, green, violet, yellow, red, and brown. Its most general form, when crystallized, is a cube, but it is frequently met with in the form of an octahedron and cubo octahedron, it also occurs in amorphous shapeless masses.”

Many of the specimens shown here are published in The Mineralogical Record 52 (2), 159-166.
In addition to Westgarth's cubes and octahedra; dodecahedron, trapezoidal icositetrahedron, trisoctahedron, tetrahexahedron and hexoctahedron forms also occur, often in combination, as shown in the images below. The dominant forms may change during crystal growth with earlier forms recorded as "phantoms" within the final crystal (see the "Polish Prodigy Pocket" fluorites illustrated below).

Twins in fluorite are fascinating, involving a 180 (or 60 degree) rotation around [111] and interpenetration of the two twin members. Increasing crystal complexity makes penetration twins challenging to interpret (e.g. see the "Fluorite Berry" twin from Colorado illustrated below). Pseudohexagonal penetration twins involving flattened cube-octahedral forms (often with several other forms present) have been widely misidentified as spinel law contact-twins, but they lack the diagnostic composition plane. Genuine spinel contact-twins in fluorite are very rarely seen and a single example is shown here involving cube-dodecahedral crystals from Naica, Mexico.