Ferrosilicon is produced by reduction of?silica?or?sand?with?coke?in the presence of iron. Typical sources of iron are?scrap iron?or?millscale. Ferrosilicons with silicon content up to about 15% are made in?blast furnaces?lined with acid?fire bricks. Ferrosilicons with higher silicon content are made in?electric arc furnaces. The usual formulations on the market are ferrosilicons with 15%, 45%, 75%, and 90% silicon. The remainder is iron, with about 2% consisting of other elements like aluminium and calcium. An overabundance of silica is used to prevent formation of?silicon carbide.?Microsilica?is a useful byproduct.