Both calcination methods produce material that falls under this heading, so classification is not affected. However, flux calcination with a fluxing agent converts more amorphous silica to crystalline cristobalite, raising the crystalline silica content. Buyers in food, beverage, and pharmaceutical filtration typically specify which grade is acceptable, and safety data sheets must reflect the crystalline silica level for regulatory compliance.

The specific gravity ceiling of 1 is the defining physical criterion that separates lightweight fossil-meal products — whose porous, low-density structure makes them effective filter aids and fillers — from denser silica minerals classified elsewhere. Importers should obtain supplier density certifications to confirm the material meets this threshold, particularly for blended or partially processed lots.