6902.10 - Containing by weight, singly or together, more than 50 percent of the elements magnesium, calcium or chromium, expressed as MgO, CaO or Cr2O3:

This HTS category, 6902.10, encompasses refractory ceramic constructional goods primarily composed of specific elements. The defining characteristic for classification within this subheading is that these materials, when expressed as their respective oxides (MgO, CaO, or Cr2O3), must constitute more than 50 percent by weight, either individually or in combination. This includes a range of products like bricks, blocks, and tiles designed to withstand high temperatures and thermal shock, commonly found in industrial furnaces, kilns, and incinerators.

It is crucial to distinguish this category from its siblings. Subheading 6902.20 covers similar refractory ceramic goods, but its classification hinges on a high content of alumina (Al2O3) or silica (SiO2), or a mixture of these. Therefore, if the dominant refractory elements are magnesium, calcium, or chromium oxides, classification falls under 6902.10, not 6902.20. Subheading 6902.90 serves as a residual category for other refractory ceramic constructional goods not meeting the criteria of 6902.10 or 6902.20.

Within 6902.10, further subdivisions exist to provide more granular classification. The subcategories, 6902.10.10.00 for magnesite bricks and 6902.10.50.00 for "Other," allow for the specific identification of different types of refractories based on their primary magnesium-containing constituent or other combinations of the specified elements. This breakdown facilitates accurate record-keeping and tariff application for a diverse array of high-performance refractory materials.