Spheroidal weathering of columnar-jointed basalt of the Ogura lava in the Takurayama Volcano, western Japan

摘要

Spheroidal weathering is an important form of rock weathering and has been attributed to chemical weathering from joint surfaces. However, the effects of the original rock structures on the processes of spheroidal weathering have not been well addressed. A columnar-jointed basalt contains primary structures that resulted from cooling, which exerted strong controls on the development of weathering with hard crusts. The primary structures were small-pore-size layers beneath the surfaces of columnar joints and some cross joints. Weathering of plagioclase was less intense in the small-pore-size layers, resulting in the exfoliation of surface parts of the layers and internal cracks.