Classification of micronised zircon sand as a mineral substance shifts tariff treatment from prepared opacifier to mineral goods. Micronised zircon sand marketed as an opacifier undergoes purification and ultra fine grinding (micronisation) without chemical transformation; micronisation is a physical size reduction to fit the product for opacifier use and is not a metallurgical process. Consequently, the Board confirms classification of micronised zircon sand as a mineral substance under 2505.00 of the Central Excise Tariff (NES), and directs settlement of pending disputes and notification to field formations and trade.