|Fluorite Ball Crystal. Collection & photo: Roger Lang
Very nice translucent fluorite ball on a yellowish calcite crystal in a quartz geode in trapp basalt. The diameter of the large fluorite ball.
The specimen in the photo is From: Mahodari, Sinnar, Nashik District, Maharashtra, India
Fluorite is a mineral usually very appreciated by mineral collectors. Its name comes from the Latin "fluere" (flow) because its melting point is quite low for a mineral and is used as a flux. This is a very common hydrothermal mineral, it is also found in some pegmatites, in the alpine clefts and in fumarolic products. It often takes the form of cubes, cubo-octahedra, octahedra, rarely dodecahedra or hexahedra, it can also be botryoidal. The colors are extremely varied and depend on the nature of the trace elements that substitute punctually calcium atoms.
Color: Green, Blue, White, Yellow, Red, Black, Purple, Pink, Orange, Brown
Crystal system: Cubic crystal system
Chemical formula: CaF₂
Hardness (Mohs hardness scale): 4
The "Frenkel defect" is the name usually given by mineral collectors to a special coloring that follows the direction of a large diagonal of a fluorite cube (green on the left photo of the sample that comes from the La Barre Mine in Puy-de-Dôme, France), whose most spectacular observation is perpendicular to one side of the cube.