16.36: Fluorite
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Fluorite | |
---|---|
Chemical composition | CaF2alcium fluoride |
Crystal system | Cubic |
Habit | Octahedral, cubes, interpenetrant twins |
Cleavage | Perfect, octahedral |
Fracture | Conchoidal |
Hardness | 4 |
Optic nature | Isotropic |
Refractive index | 1.434 |
Birefringence | Isotropic |
Dispersion | Very low, 0.007 |
Specific gravity | 3.18 |
Lustre | Poor vitreous |
Fluorescence | Bluish-white, purple (LW) |
Figure \(\PageIndex{1}\): Fluorite with Barite and Galena
Elmwood Mine, Carthage, Tennessee
Figure \(\PageIndex{2}\): Fluorite with Sphalerite and Barite
Elmwood Mine, Carthage, Tennessee
Figure 16.36.3: Faceted purple fluorite
Figure 16.36.4: Green Fluorite
Westmoreland, New Hampshire
Figure 16.36.5: Faceted Green Fluorite; 229 carats
Figure 16.36.6: Fluorite
Figure 16.36.7: Yellow Fluorite Crystals
Clay Center, Ohio
Figure 16.36.8: Yellow Fluorite Faceted
847.4 carats and 84.7 carats
Figure 16.36.9: Yellowish Green Fluorite
Diagnostics
Thermoluminescence
Fluorite may luminesce when heated. The stored energy from UV radiation is released if heated to a certain temperature and the effect depends on the amount of stored energy.
One can see this when a small amount of fluorite is placed on a teaspoon and heated over a candle for a few minutes (in a dark room).
Material from Telemark, Norway will show a blue-green thermoluminescence.
Optical phenomena
Color change
Color change fluorite has been reported with a change from blue to purple (much like some color change garnet).