Tellurium has two forms, crystalline and amorphous. Crystalline tellurium is a silvery-white and brittle metal (or technically a metalloid) with a typical metallic luster. Amorphous tellurium is a black-brown powder prepared by precipitating it from tellurium or tellurous acid solution. Tellurium is very corrosive to copper, iron, and stainless steel in the molten form. Tellurium also has semiconductor properties.