As a dense metamorphic rock with silica grains that are strongly fused, quartzite exposed on rocky shores is generally resistant to marine erosion. The longevity of quartzite coasts compared to those formed by other rock types is underscored by the preservation of many former islands that retain notable topographic relief as inliers of Archean and Proterozoic quartzite surrounded by Paleozoic marine strata in North America and Western Australia. Among the few places where modern rocky shores composed principally of quartzite may be studied with regard to marine erosion, Hongdo in the Yellow Sea off the southwestern Korean peninsula is a natural laboratory where intersection of structural geology, coastal geomorphology, oceanography, sedimentology, and climate converge to demonstrate how a quartzite island evolves through time. Although small in size (6.87 km2), Hongdo is open to the ocean on all sides. The island’s structure as an asymmetrical anticline permits a wide range of attack angles for seasonal storms to work against variable thicknesses in bedding as well as intervals of rock cleavage perpendicular to original bedding. Along the island’s 20.8-km perimeter, Mongdol Beach on the west side is the only place where eroded clasts accumulate, typically as quartzite cobbles. Size and shape analyses on multiple samples show that rock partings of both kinds (bedding and cleavage) play a roll in contemporaneous clast development. All clasts are elongate in shape, but many clasts that originate from zones where cleavage is predominant tend to be less ellipsoidal in form. Orientation of Mongdol Beach indicates that the principal agent of coastal erosion relates to the frequent monsoonal storms that reach the island from the Asian continent in the northwest during the late fall and winter months of November through March. Fewer but more intense, typhoons may arrive from the southeast during August and September. The island’s eastern coast is better shielded against wave surge coming from this direction by the steeply dipping eastern limb of the anticline.