Yim Tin Tsai
Ma Wan surface rocks are mostly volcanic rocks called Yim Tin Tsai Formation. This is a coarse ash crystal tuff containing lapilli. Some layers of fine volcanic ash are found in the far north of the island. The contained mafic minerals are biotite and amphibole. The tuff contains mostly quartz and alkali and plagioclase feldspar. Other minerals include apatite, magnetite, monazite and zircon.