2528.00.00.05 - Natural sodium borates and concentrates thereof (whether or not calcined)

This HTS category, 2528.00.00.05, encompasses natural sodium borates and their concentrates, including those that have been calcined. These are mineral products primarily composed of sodium and boron, found in naturally occurring deposits. Examples include natural sodium borates like tincal, kernite, and ulexite, as well as their processed forms that concentrate the borate content. The key characteristic is their origin as naturally occurring minerals, distinct from synthetically produced borates.

It is crucial to distinguish this classification from its sibling categories. Specifically, 2528.00.00.10 covers natural *calcium* borates, such as colemanite and meyerhofferite, which are chemically different due to the presence of calcium instead of sodium. The "Other" category (2528.00.00.50) serves as a residual classification for any natural borates not otherwise specified within this heading.

As this is a leaf node within the HTS, there are no further subcategories to introduce. Therefore, classification within 2528.00.00.05 relies on confirming the natural origin and the primary component being sodium borates or their concentrates. The parent category clarifies that natural boric acid containing a high percentage of H3BO3 falls under a different, more specific classification.