The key distinction is raw material: 6901 covers bricks and tiles made from siliceous fossil meals such as diatomite, kieselguhr, or tripolite, while 6902 covers refractory constructional goods made from other materials (alumina, magnesia, chromite, etc.). If the dominant mineral is a siliceous fossil meal, classification falls under 6901 regardless of the article's refractory function.

Primary buyers include industrial furnace and kiln operators who use diatomite-based bricks for lightweight insulating linings, as well as filtration equipment manufacturers who rely on the porous structure of siliceous earths. Specialty chemical processing and food-grade filtration plants are also common end users.