Subheading 251010 covers unground phosphate rock — material in its mined, uncrushed, or only roughly broken state. Subheading 251020 covers ground material, meaning it has been milled or otherwise reduced in particle size. The distinction matters commercially because ground rock is ready for direct chemical processing, while unground material requires additional milling. Both subheadings cover the same mineral types; only the processing state differs.

Heading 2510 covers only the natural mineral forms — phosphate rock as mined and at most ground. Once the rock is chemically processed to produce phosphoric acid, superphosphate fertilizers, or other phosphate compounds, the products leave this heading and are classified in the chapters covering inorganic chemicals or fertilizers, depending on the form. The boundary is chemical transformation: physical size reduction stays in 2510; chemical reaction moves the product out.