Eruptions at Haruj have produced relatively uniform volcanic rocks consisting of olivine basalt that forms a tholeiitic to alkali basalt suite; the alkaline basalts were originally interpreted as hawaiite. Minerals contained within the volcanic rocks include clinopyroxene, olivine, plagioclase and titanomagnetite, with secondary calcite, iddingsite, serpentine and zeolite. Based on compositional differences, the volcanic rocks have been subdivided into an older and a younger family.