Fluorite (Fluorite)

CaF 2

[Chemical composition] Rare earth elements (mainly Th, Ce, U) and Y can replace Ca in the form of isomorphism, or can be adsorbed in the fissures of fluorite , or form a solid inclusion in the form of solid inclusions. Stone. In addition, it also contains a mixture of Fe 2 O 3 , Al 2 O 3 , SiO 2 , and a bituminous substance (blackish black, heated and odorous).

[crystal structure] equiaxed crystal system; 360 screenshot20170720101852723 a 0 = 0.545 nm; Z = 4.

Picture 21

Figure H-23 Crystal of fluorite

Picture 22

Figure H-24 Twin crystal of fluorite

(quoted from Pan Zhaoyu et al., 1993)

[Form] The crystal is often in the cube {100}, followed by the octahedron {111}, a few have the rhombohedron {110}, sometimes the tetrahexahedron {210} and the hexahedron {421}, etc. (Fig. H-23 )). The cubic crystal face often has a parquet floor strip parallel to the rib. Often (111) into interspersed twins (Figure H-24). The aggregates are grainy, massive, spheroidal, and occasionally earthy blocks. The fluorite crystal morphology has a characterization characteristic that varies with the pH and ion concentration of the medium. Crystallization in alkaline solution, F - ions play a dominant role, and the development of a large network density F- ions surface plane {100} crystal into cubes; crystallization solution in a neutral, Ca 2+ and F - a considerable role, The crystal plane with the highest density of surface network composed of Ca 2+ and F - is {110} into a rhombohedral dodecahedron; in an acidic medium, Ca 2+ plays a dominant role and develops the crystal plane with the highest density of Ca 2+ surface network. 111} and form an octahedron.

[Physical properties] Various colors, colorless, white, yellow, green, blue, purple, purple black and black, the coloring mechanism is also very complicated, mainly for color centering, that is, radiation damage caused by radioactive elements The lattice defect and Na + , K + → Ca 2+ cause F - absent to form a color center. When heated, it can fade; glass luster. Cleavage {111} is complete. Hardness 4. The relative density of 3.18 (comprising Y, Ce by increasing the relative density, relative density yttrium fluorite 3.3). Crisp. The melting point of 1270 ~ 1350 ° C. Fluorite has a spin-rotation property, and the thermal luminescence intensity is related to the rare earth content and the Na content.

[genesis and production] mainly hydrothermal type, but also sedimentary type.

[Identification characteristics] According to its crystal form, {111} complete cleavage, hardness 4 and various light colors and other features are easy to identify, in addition to fluorescence, thermo-optic test can also assist in identification.

[Uses] as a flux in the metallurgical industry, used in making a fluoride (such as hydrofluoric acid), manufactured by the opaque white glass and enamel and glass ceramics in the chemical industry. It can also be used in optical instruments and engraving processes.

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