| General Information |
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| Varieties/Types: | |
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| Other Names/Trade Names: | |
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| Chemical Formula | Michael O’Donoghue, Gems, Sixth Edition (2006) More from other references |
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| Fluorite Treatments |
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The blue to deep blue to black color seen in some fluorites is derived from a color center, the F-center. This involves an electron-center precursor, and a missing fluorine atom in the fluorite, CaF2. An electron liberated by irradiation or other processes (Nassau, 1983) from a hole-center precursor can be trapped at the fluorine vacancy to become the electron color-center. Many other color-centers are known in fluorite, including those producing yellow, green, violet, pink, and other colors; some of these are stable to light, others are not.
The color of most of these color centers can be lightened by a gentle heating to 100-150°C and is totally removed at 200-300°C. This process has long been used to lighten some excessively dark blue john, a deep blue, banded massive fluorite found in Derbyshire, England, and used for carved ornamental objects.
Although colored impregnation and dyeing do not seem to have been reported, their use on massive fluorite would not be too surprising. Plastic impregnation is detected by careful examination; the heat and irradiation treatments are not identifiable - Nassau (1984)
Artificial irradiation of some colorless to pale green fluorite produces a typical "iolite blue", "tanzanite", "purplish-blue", also dark blue, dark green and bright purple - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 9 |
| Physical Properties of Fluorite |
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| Mohs Hardness | 4Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Specific Gravity | 3.00 to 3.25Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Tenacity | BrittleArthur Thomas, Gemstones (2009) |
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| Cleavage Quality | PerfectHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Fracture | IrregularArthur Thomas, Gemstones (2009) |
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| Optical Properties of Fluorite |
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| Refractive Index | 1.432 to 1.436Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Optical Character | IsotropicUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Dispersion | 0.006Arthur Thomas, Gemstones (2009) |
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| Colour |
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| Colour (General) | Colourless, pink, red, brown, green, yellow, blue, violet. Colour change: blue/violet, smoky brown/lilacUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Colour (Daylight) | Smoky-brown (from India)Michael O’Donoghue, Gems, Sixth Edition (2006) |
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| Colour (Incandescent Light) | Mauve (from India)Michael O’Donoghue, Gems, Sixth Edition (2006) |
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| Causes of Colour | Violet, Mie scattering on calcium microcrystallites. Blue Y3+ + F vacancy +2 electrons. "Emerald" green ("chrome fluorite"), Sm2+. Yellowish green, color center containing Y3+ and Ce associated with an F vacancy. Yellow, O3 color center = O2 substituting for fluorite. Pink, YO2 color center (Y3 + O3-2). Color change, Y3+ associated color center and Sm2+, with minor influence of a Ce3+ associated color centerW. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011) |
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| Transparency | Transparent,Translucent,OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Lustre | VitreousArthur Thomas, Gemstones (2009) |
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| Fluorescence & other light emissions |
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| Fluorescence (General) | Commonly blue to violet or greenUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) |
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| Fluorescence (Long-Wave UV) | Inert to strong blue to greenHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Phosphorescence | Some specimens phosphoresceMichael O’Donoghue, Gems, Sixth Edition (2006) |
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| Triboluminescence | May show triboluminescenceMichael O’Donoghue, Gems, Sixth Edition (2006) |
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| Thermoluminescence | May show thermoluminescenceMichael O’Donoghue, Gems, Sixth Edition (2006) |
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| Crystallography of Fluorite |
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| Crystal System | IsometricHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Habit | Cubic, massiveArthur Thomas, Gemstones (2009) |
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| Geological Environment |
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| Where found: | Fluorite occurs in low-to-high temperature hydrothermal veins, granites and granite pegmatitesMichael O’Donoghue, Gems, Sixth Edition (2006) |
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| Inclusions in Fluorite |
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| Negative crystals, two- or three-phase inclusions, healing cracks, crystal inclusions - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 1 |
| Further Information |
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| Mineral information: | Fluorite information at mindat.org |
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| Significant Gem Localities |
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| France | | |
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 412 | | Myanmar | | |
| Ted Themelis (2008) Gems & mines of Mogok | |
| Ted Themelis (2008) Gems & mines of Mogok |
- Pein-Pyit (Painpyit; Pyan Pyit)
| Ted Themelis (2008) Gems & mines of Mogok | |
| Ted Themelis (2008) Gems & mines of Mogok | | UK | | |
| Fisher, J.E., and L. Greenbank, 2000, The Rogerley Mine, Weardale, County Durham, England. Rocks and Minerals, 75(1), 54-61. | |
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 412 | |
| [var: Blue John] [www.thamesvalleyminerals.com] | |
| [var: Blue John] Fluorite: The Collector's Choice. Extra Lapis English No. 9 | | USA | |
- Cave-In-Rock Mining Sub-District
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 412 |
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