Heading 2839 covers simple alkali metal silicates (sodium, potassium, lithium). Heading 2842 captures double or complex silicates—compounds where silicon is combined with two or more metal cations, including aluminosilicates. If the compound contains aluminum or another metal alongside silicon, 284210 is the likely classification, but a binding ruling from CBP is advisable for novel or borderline materials.

Subheading 284290 covers salts of inorganic acids and peroxoacids that are not azides and are not more specifically provided for elsewhere in the chapter. Examples include fulminates, thiocyanates, and certain peroxosalts. Because this is a residual provision, classification requires systematically ruling out all more specific headings first.