The principal rock is dacite, rich in potassium. The rocks have a porphyric appearance and contain few vesicles. They are also very rich in crystals, with the dominant phenocryst-forming minerals being biotite, hornblende and plagioclase. Less important are allanite, apatite, clinopyroxene, olivine, orthopyroxene, quartz, sphene and zircon. The groundmass contains plagioclase, pyroxene, silicon dioxide and oxides of iron and titanium. The composition of Ciomadul's rocks has been fairly constant throughout its evolution albeit with two shifts 1 million and 650,000 years before present, and this diversity of its components indicate that the genesis of Ciomadul magmas involved mixing between felsic and mafic magma.