25.18 Dolomite, whether or not calcined or sintered, including dolomite roughly trimmed or merely cut, by sawing or otherwise, into blocks or slabs of a rectangular (including square) shape.
Dolomite is a natural double carbonate of calcium and magnesium. The heading covers crude dolomite as well as calcined and sintered dolomite. Dolomite is calcined at a temperature range of 700 ¡ÆC - 1000 ¡ÆC to convert it into magnesium and calcium oxides by releasing carbon dioxide. On the other hand, sintered dolomite is obtained by heating dolomite to a temperature range of 1700 ¡ÆC - 1900 ¡ÆC when it becomes a refractory material. The heading also includes dolomite which has been roughly trimmed or merely cut, by sawing or otherwise, into blocks or slabs of a rectangular (including square) shape. However, the heading does not cover crushed dolomite for concrete aggregates, road metalling or railway ballast (heading 25.17) or dolomite ramming mix (heading 38.16).
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