Difference between revisions of "Fluorspar"
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Revision as of 14:17, 24 June 2013
|Infobox on Fluorspar|
|Example of Fluorspar|
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Fluorite is a mineral with a veritable bouquet of brilliant colours. Fluorite is well known and prized for its glassy luster and rich variety of colours. The range of common colours for fluorite starting from the hallmark colour purple, then blue, green, yellow, colourless, brown, pink, black and reddish orange is amazing and is only rivaled in colour range by quartz. Intermediate pastels between the previously mentioned colours are also possible. It is easy to see why fluorite earns the reputation as "The Most Colourful Mineral in the World".
The many colours of fluorite are truly wonderful. The rich purple colour is by far fluorite's most famous and popular colour. It easily competes with the beautiful purple of amethyst. Often specimens of fluorite and amethyst with similar shades of purple are used in mineral identification classes to illustrate the folly of using colour as the sole means to identify minerals.
The blue, green and yellow varieties of fluorite are also deeply coloured, popular and attractive. The colourless variety is not as well received as the coloured varieties, but their rarity still makes them sought after by collectors.
Fluorite (also called fluorspar) is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Crystal twinning is common and adds complexity to the observed crystal habits.
The word fluorite is derived from the Latin root fluo, meaning "to flow" because the mineral is used as a flux in iron smelting to decrease the viscosity of slags at a given temperature. This increase in fluidity is the result of the ionic nature of the mineral.
Fluorite is a colourful mineral, both in visible and ultraviolet light, and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so lenses made from it exhibit less chromatic aberration, making them valuable in microscopes and telescopes. Fluorite optics are also usable in the far-ultraviolet range where conventional glasses are too absorbent for use.
There are three principal types of industrial use for natural fluorite, commonly referred to as "fluorspar" in these industries, corresponding to different grades of purity. Metallurgical grade fluorite (60–85% CaF2), the lowest of the three grades, has traditionally been used as a flux to lower the melting point of raw materials in steel production to aid the removal of impurities, and later in the production of aluminium. Ceramic grade fluorite (85–95% CaF2) is used in the manufacture of opalescent glass, enamels and cooking utensils. The highest grade, "acid grade fluorite" (97% or more CaF2), accounts for about 95% of fluorite consumption in the US where it is used to make hydrogen fluoride and hydrofluoric acid by reacting the fluorite with sulfuric acid.
Internationally, acid-grade fluorite is also used in the production of AlF3 and cryolite (Na3AlF6), which are the main fluorine compounds used in aluminium smelting. Alumina is dissolved in a bath that consists primarily of molten Na3AlF6, AlF3, and fluorite (CaF2) to allow electrolytic recovery of aluminium. Fluorine losses are replaced entirely by the addition of AlF3, the majority of which will react with excess sodium from the alumina to form Na3AlF6.
The uses of fluorite are as follows:
- Ornamental uses.
- As flux in the manufacture of steel.
- In the making of opalescent glass.
- As enamels for cooking utensils.
- As hydrofluoric acid.
- As elements in place of glass in some high performance telescopes and camera lens.
Natural fluorite mineral has ornamental and lapidary uses. Fluorite may be drilled into beads and used in jewelry, although due to its relative softness it is not widely used as a semiprecious stone.
Melting point: 1350°C.
Shipment / Storage / Risk factors
Fluorspar is a mineral cargo which is mined and then is subjected to a washing process.
The mineral consists of finely divided particles and is occasionally shipped at a too high moisture content, of the order of 9 to 10 per cent. In such a form the mineral is liable to liquefy during ocean transport and this liquefaction may result in shift of cargo. Under extreme circumstances this shift of cargo may result in capsize of the carrying vessel.
There have been several incidents of cargo shift during the carriage of fluorspar. In one instance the vessel capsized, in another the list was so severe that the vessel was abandoned and later grounded, and another leaned against the quay wall during loading.
Unfortunately the masters of the vessels in the incidents were not presented with certificates relating to transportable moisture limit, but received certificates of the total moisture content only. They were not able to determine if the cargo was safe to carry in accordance with the information provided to them and as recommended by the IMO Code of Safe Practice.
Shippers of cargoes liable to liquefy normally test their production at regular intervals to determine the transportable moisture limit. The properties of minerals from the same mine or seam within that mine should be fairly constant, and this would include the transportable moisture limit. However, it has been noted that there can be a variation of the transportable moisture limit within a particular cargo provided for shipment. These variations have been observed in tests for transportable moisture limit, screening behaviour, appearance, etc.
To ensure safe shipment of these cargoes the master should demand certificates relating to transportable moisture limit and total moisture content of the cargo immediately before it is loaded to his vessel. If the actual moisture content is in excess of the transportable moisture content, the cargo should not be loaded unless the vessel is specially constructed or fitted.
Fluorspar is a dusty commodity usually shipped in powder form in bags or in solid blocks. Used in the manufacture of glass and various branches of metallurgy, also in the manufacture of hydrofluoric acid. Contact with salt water may be detrimental and prevent the material being used for its intended purpose; such damaged fluorspar should have a value in other directions. Damage by fresh water causes little loss in value except that some users may object to the increased moisture content, but this may be reduced by drying. Is subject to loss in weight due to seepage of contents, particularly if not packed in double bags. If shipped in lumps it may become powdery, with resultant loss.
Please check the IMSBC (International Maritime Solid Bulk Cargoes Code) for overseas transport information.