Antimony(III) oxide is the most important commercial compound of antimony, a brittle, silvery-white semimetal that conducts heat poorly. Antimony trioxide is found in nature as the minerals stibnite. It is synthetically produced by roasting antimony metal in a furnace with oxygen present or recycled from lead-based batteries. Antimony trioxide is predominantly used in polymer where resistance to ignition and flammability are required. Antimony(III) oxide is a synergistic of halogens, typically chlorine and bromine based, necessary to achieve performance levels in compliance with European labeling directives and at the same time pass specific tests for fireproof materials such as UL94 or in the automotive sector. Sb2O3 is also used as a catalyst for PET manufacture, as a frictional additive in automotive brake linings, as a clarifier for glass, as an opacifier for enamels, and in ceramic and textile applications.