From Longman Dictionary of Contemporary Englishfirebrickfire‧brick /ˈfaɪəˌbrɪk $ ˈfaɪr-/ noun [countable] TBa brick that is not damaged by heat, used in chimneys
Examples from the Corpus
firebrick• The blow pipe extends from the bellows through the firebrick wall of the forge to the bottom of the fire. 