2839.90 - Other:

This category, HTS 2839.90, encompasses silicates, specifically commercial alkali metal silicates, that are not classified under the preceding subheadings within 2839. It serves as a residual category for these chemical compounds. The key characteristic is their classification as alkali metal silicates, meaning they contain silicon, oxygen, and at least one alkali metal (such as lithium, sodium, potassium, rubidium, or cesium) bonded to oxygen or silicon.

Unlike the sibling category that specifically addresses sodium silicates, this residual "Other" category covers alkali metal silicates where the predominant alkali metal is not sodium. This would include, for example, potassium silicates, lithium silicates, or mixed alkali metal silicates where sodium is not the sole or primary alkali metal present. The defining factor remains the presence of an alkali metal and the silicate structure.

Within this residual category, further subdivisions exist to provide more granular classification. HTS 2839.90.10.00 specifically addresses silicates of potassium, distinguishing them from other alkali metal silicates. The remaining silicates not falling under potassium or other specifically defined alkali metals are then placed under the HTS 2839.90.50.00 subheading, "Other," which might encompass silicates of lithium, rubidium, cesium, or other less common alkali metal combinations.