大屯火山群十八份熔岩，位處於風化作用及蝕變作用強烈的區域。本研究共採集 25 個標本，藉由岩象、礦物相及地球化學以及風化指數方法進行分析，予以了解風化作用及蝕變作用對安山岩熔岩之影響程度，並且提出其轉變概念模式。
十八份熔岩岩性分別為兩輝玄武質安山岩以及含普通角閃石兩輝玄武質安山岩。主要的礦物組成為普通輝石、紫蘇輝石、普通角閃石及倍長石；風化作用及蝕變作用下的產物為方矽石及禾樂石。岩石環狀紋路越厚，其中硫含量越高且越接近火山噴氣位置。最後，本研究中將十八份熔岩分為 5 個風化等級，隨著風化等級增加，岩石中的矽、鋁及硫含量隨之增加。
The Shibafen lava is located in Tatun Volcano Group with intensity weathering and alteration. 25 samples are collected and analyzed by petrography, X-ray diffraction, geochemistry and weathering index. This study aims to provide the conceptual model of minerals assemblages change under the processes of weathering and alteration.
This study has two types of igneous rock including two pyroxenes basaltic andesite, and two pyroxenes basaltic andesite with hornblende. The predominant mineral assemblages are augite, hypersthene, bytownite, and hornblende, and the alteration mineral assemblages are cristobalite and halloysite. The andesite has thicker ring, which exists higher sulfur, that is near the fumarole area. Finally, the Shibafen lava is distinguished five stages by degrees of rock mass weathering. The silica, aluminum, and sulfur have higher contents as the more weathering and alteration.
