It can be described as a mafic phonolite or a potassic tephrite. Additional rocks are basanite, mugearite, picrite and tephrite. Holocene layers contain augitite, leucite basanite, potassic hawaiite and leucite tephrite. At Vesuvius it occurs as alterations from gypsum within leucite tephrite and as fumarole deposits. Horgo/Khorgo is constructed from phonolitic tephrite and its lavas range alkali basalt-basanite. Pico do Fogo consists of basanite, tephrite, phonotephrite, clinopyroxene, amphibole, magnetite, olivine, melilite and leucite. Tephrite is an igneous, volcanic (extrusive) rock, with aphanitic to porphyritic texture.