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Pumice stone is a very porous variety of volcanic rock, rough to the touch and extremely light in weight, usually whitish or grey, but sometimes brown or red. The heading also covers crushed pumice (bimskies).
Emery is a dense rock formed of small hard aluminium oxide crystals mixed with iron oxide and particles of mica. It is often presented in rock form for use as an abrasive powder after simple crushing. Crushed emery is a dirty brown powder interspersed with occasional glittering grains; a magnet attracts the particles of iron oxide.
Natural corundum is also composed largely of aluminium oxide but, unlike emery, it is often presented in bags, in the form of more or less fine grains. Ground or crushed corundum is mainly composed of small white granules with a few black or yellow particles. Natural corundum remains classified in this heading even if it has been heat treated.
Other natural abrasives include the tripoli known as "rotten‑stone", an ash grey product used as a mild abrasive or for polishing, and garnet (including dust and powder) other than that of Chapter 71. The natural abrasives of this paragraph remain classified in this heading even if they have been heat‑treated; natural garnet, for example, is sometimes heat‑treated after grading to improve its capillarity and hardness.The heading does not include : (a) Abrasive materials referred to in other headings of this Chapter. (b) Precious or semi‑precious stones (e.g., ruby, sapphire) of heading 71.03. (c) Artificial abrasives such as artificial corundum (heading 28.18), silicon carbide (heading 28.49) and synthetic precious or semi‑precious stones (heading 71.04). (d) Dust and powder of natural or synthetic precious or semi‑precious stones (heading 71.05).
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