2528.00.00 - Natural borates and concentrates thereof (whether or not calcined), but not including borates separated from natural brine; natural boric acid containing not more than 85 percent of H3BO3 calculated on the dry weight

This HTS category, 2528.00.00, encompasses natural borates and their concentrated forms, excluding borates derived from natural brine. It also includes natural boric acid that contains no more than 85 percent H3BO3 by dry weight. The defining characteristic is the origin of these borates as naturally occurring minerals, which are then either directly used or further concentrated. This classification falls under Chapter 25, which deals with mineral products, specifically those that are not metals.

Distinguishing this category from its siblings within Section V (Mineral Products) is crucial. While siblings at the same level might represent other salts, sulfur, earths, stones, or plastering materials, 2528.00.00 specifically isolates naturally occurring boron compounds. It differentiates itself from processed or synthetic boron compounds that would be classified elsewhere based on their chemical composition or manufacturing origin. The inclusion of "natural boric acid" with a specific percentage threshold also serves to delineate it from higher concentrations or artificially produced boric acid.

The subcategories under 2528.00.00 further refine the classification based on the chemical composition of the natural borates. "Natural sodium borates and concentrates thereof" covers common borax minerals, while "Natural calcium borates" addresses other significant natural boron minerals. The residual category, "Other," is available for any natural borates or their concentrates that do not fall into the more specific sodium or calcium classifications, ensuring comprehensive coverage within this product group.