Huayu is the westernmost islet in the Penghu Islands. The rock formations on this islet are different from those on other islets in Penghu. The rocks on the islet are all acidic to neutral igneous rocks, mainly composed of neutral andesiteacidic rhyolite. As these rocks are moreless erodedaltered, it is not easy to accurately determine their true composition. Huayu was formed 95 million years ago,it was metamorphosed 65 million years ago by extremely low-temperature hot water, with a metamorphism temperature between 250300 °C. Therefore, the rocks containing quartzfeldspar are often referred to as felsic porphyry. Among the rocks exposed in Huayu, porphyry is the most common. It is dark greenhas phenocrysts of quartzfeldspar. Quartz porphyry develops on the southeast coast, north coastsouthwest coast. Due to severe weathering, the color becomes yellow-graygray-white. Feldspar porphyry is distributed in the north to northwest of Huayu Village,is light cyanlight gray. The most widely distributed rocks on the islet are porphyritic andesitelava volcanic breccia, as well as tuffaceous andesite. Andesite is interspersed with quartz andesite veins, felsic porphyryblack basaltlamprophyre. Huayu is the oldest islet in Penghu,lava has flaky joints, which peel off like scales after weathering. Among them, feldspar is more likely to become clay, partly due to the hot water mass exchange of ancient volcanoes to generate kaolinite, which is the raw material for ceramic production. The andesite collected by this center is from Huayu.