2519 - Natural magnesium carbonate (magnesite); fused magnesia; dead-burned (sintered) magnesia, whether or not containing small quantities of other oxides added before sintering; other magnesium oxide, whether or not pure:

Heading 2519 encompasses various forms of magnesium oxide and magnesium carbonate derived from natural sources or manufactured processes. This category includes natural magnesium carbonate, commonly known as magnesite, which is a naturally occurring mineral. It also covers fused magnesia, produced by melting magnesia at very high temperatures, and dead-burned (sintered) magnesia. Dead-burned magnesia is a refractory material produced by heating magnesium carbonate or oxide to a high temperature, rendering it largely inert and stable. Small quantities of other oxides may be added before sintering to modify properties, but the primary component remains magnesium oxide. Finally, this heading extends to other forms of magnesium oxide, regardless of their purity.

Unlike sibling categories within Section V that deal with other minerals and raw materials such as salt, sulfur, earths, stones, lime, and cement, Heading 2519 specifically focuses on magnesium-based mineral products. For instance, while Heading 2518 covers magnesium carbonate and oxide in their raw mineral forms as magnesite and dolomite respectively, Heading 2519 goes further to include processed and manufactured forms like fused and dead-burned magnesia, as well as other refined magnesium oxides.

Within Heading 2519, further subdivision is provided to distinguish between the natural form of magnesium carbonate and other magnesium oxide products. Subheading 2519.10.00.00 specifically covers natural magnesium carbonate (magnesite). All other forms of magnesium oxide, including fused and dead-burned varieties, and other magnesium oxides not specifically classified elsewhere under this heading, fall under the "Other" subheading, 2519.90. This hierarchical structure allows for precise classification based on the material's origin and processing method.