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25.29 Feldspar; leucite; nepheline and nepheline syenite; fluorspar.
Feldspar, leucite, nepheline and nepheline syenite are composed of complex silicates of aluminium and alkali or alkaline earth metals. They are used as fluxes in the ceramic industry. The heading excludes feldspathic sands (heading 25.05). Fluorspar (or fluorite) is natural calcium fluoride occurring as solid masses streaked with varied colours or in agglomerated crystals of various colours; it is principally used in the manufacture of hydrofluoric acid and as a flux for metallurgical purposes. The heading also covers fluorspar obtained from the mineral by a heat treatment which causes the product to break up into its constituent particles; as these differ in size, simple screening then permits removal of part of the silica content. The heading excludes feldspar or fluorspar in the form of precious or semi precious stones (Chapter 71).
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