Fluorite color

All varieties of color are mainly connected with two main absorption bands in the violet and yellow parts of the spectrum. The secondary bands are also present - in blue and green diapasons. The main absorption bands are connected with F and M-centers. The first one is anion vacancy, which traps electrons and the second is two neighboring anion vacancies with two trapped electrons. The short-wave band in fluorite is generated by mutual absorption of F and M-centers, while the long-wave band is connected with M-center absorption only. In the green varieties the REE (Sm ", Yb and Dy ) are also appreciable. Besides that, the centers O2, O3 and (Y, TR)02 sometimes have influence with resulting yellow and pink colors (Platonov 1979 Krasilschikova et al. 1986). 

The mineral fluorite, CaF2, in Figure 13-5 has a cubic crystal structure and often cleaves to form nearly perfect octahedra (eight-sided solids with equilateral triangular faces). Depending on impurities, the mineral takes on a variety of colors and may fluoresce when irradiated with an ultraviolet lamp. 

BARYTOCALCITE. This mineral is a carbonate of barium and calcium il crystallizes in the monoclinic system but occurs massive as well. Il lias a perfect cleavage parallel to the prism and one, less perfect, parallel to the base fracture, sub-conchoidal brittle hardness, 4 specific gravity, 3.66-3.71 luster, vitreous color, white or gray or may be greenish or yellowish transparent to translucent. Barytocalcite is found in Cumberland. England, associated with barite and fluorite. 

The triboluminescence of minerals has been studied visually (see the footnotes to Table I) but only a few minerals have been examined spectroscopically. There are a few clear examples of noncentric crystals, such as quartz, whose emission is lightning, sometimes with black body radiation. Most of the triboluminescent minerals appear to have activity and color which is dependent on impurities, as is the case for kunzite, fluorite, sphalerite and probably the alkali halides. Table I attempts to distinguish between fracto-luminescence and deformation luminescence, but the distinctions are not clear cut. A detailed analysis of the structural features of triboluminescent and nontriboluminescent minerals may make it possible to draw conclusions about the nature and concentration of trace impurities that are not obvious from the color or geological site of the crystals. Triboluminescence could be used as an additional method for characterizing minerals in the field, using only the standard rock hammer, with the sensitive human eye as a detector. 

Titley, S. R., and P. E. Damon Investigation of Color-Centers in Fluorite with Application to Geologic Time. J. geophys. Res. 67, 4491 (1962). 

Halide Fluorite (fluorospar) CaF2 All colors 3.18 1.433 4 Perfect cleavage in four directions... 

Turns are pure CaC03. Calcium fluoride (CaF2) is the principal source of fluorine in the production of hydrofluoric acid (HF). Hydrofluoric acid is often the source of fluorine in the processes of manufacturing fluorine-containing chemicals. The mineral fluorite (CaF2) occurs in nature in several colors and is used as a gemstone. 

Sm luminescence has been reported from natural anhydrite samples (Gaft et al. 1985, 2001a Taraschan 1978) as a broad strong band at 630 nm. Other sharp bands are reported at 688, 700 and 734 nm. Sm emission has not been reported for apatite, but the ion size and valence are amenable to the Ca sites, so ultimately it may be observed via pulsed laser techniques. Sm is present in aqueous solution only under quite reducing conditions, so this may limit concentrations. Sm does occur in fluorite, and is responsible for the strong green coloration and sensitized Eu luminescence in that mineral (Robbins 1994). However, in fluorite the Sm may be created by radiation effects which reduce bound Sm ions. Yb emission has not apparently been reported in any minerals, but has been studied in borates and oxides (Blasse and Grabmaier 1994). Its... 

Figure 3-1. Fluorite unit cell and one octant of the ceU (M4/gO-module). Different orientations of the tetrahedral voids in the f.c.c. unit ceU in different colors.

The rutile and fluorite structures, shown here (anions are colored green), are two of the most common structure types for ionic compounds where the cation to anion ratio is 1 2. (a) For Cap2 and Znp2 use ionic radii, Ca (r = 1.14 A), Zn " (r = 0.88 A), F (r = 1.19 A), to predict which compound is more likely to crystallize with the fluorite structure and which with the rutile structure, (b) What are the coordination numbers of the cations and anions in each of these structures ... 

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