안산암질 is a type of volcanic rock that is primarily composed of basalt. It is formed from the rapid cooling of lava that has a relatively low viscosity, allowing gases to escape easily. This rock is commonly found in areas with volcanic activity and is characterized by its dark color and fine-grained texture. The term "안산암질" is often associated with the geological features of the Ansan region in South Korea, where such volcanic rocks are prevalent. These rocks play a significant role in understanding the region's volcanic history and contribute to the study of igneous rocks in geology.