Petrology and geochemistry of an unusual tridymite-hercynite xenolith in tholeiite from southeastern China

A rare variety of Fe-Al-rich xenolith, tridymite-hercynite rock, was entrained in the Cenozoic basalt from Niutoushan, southeastern China. The tridymite-hercynite rock consists of hercynite (40–50%), tridymite (35–45%), ilmenite (≈2%), and glass (10–20%). Mineral grains are smaller than 0.05 mm with a granular texture. Compared to “normal” igneous rocks, this tridymite-hercynite rock has higher FeO, Al2O3, and lower SiO2 CaO, MgO, and alkalis (Na2O + K2O).