Dolomite, Not Calcined or Sintered

Raw, uncalcined dolomite — the calcium magnesium carbonate mineral — enters US commerce primarily as a refractory raw material, flux in steelmaking, and agricultural soil amendment, with its magnesium content and purity grade driving commercial value. Classified under a single tariff line (2518100000), it is distinguished from calcined or sintered dolomite (heading 251820) by the absence of heat treatment, which preserves its natural carbonate chemistry. Canada is the leading supplier, with Italy, Mexico, Spain, and Germany also among the top sources. Importers should confirm that the material has not undergone calcination, as even partial heat treatment shifts classification to 251820.