Only a fire-resistant brick should be used in chimney construction. There is a big difference between fire bricks and normal bricks. Normal bricks are made of clays and slates that are shaped and manufactured to withstand small amounts of heat.
Fire bricks are made of fireclay and other components to withstand large amounts of heat. The material prevents the heat from radiating beyond the area to which it was exposed. Refractory mortar or a specially formulated mixture of mortar and fireclay should be used in the manufacture of the fireplaces.