Soils developing on the 120 ka terrace of the Rio Parrita near the Pacific coast of Costa Rica contain basalt clasts with well-developed weathering rinds. These rinds are the result of in situ, isovolumetric chemical weathering of the parent clast. This weathering rind system can be viewed as a miniature saprolite-forming environment where the processes occurring at the rind/core interface are analogous to processes occurring at larger landscape scales at the saprolite/bedrock interface. Physical and chemical characteristics of the rind/core interface have been examined in two clasts with different textures using scanning electron microscopy (SEM), SEM energy dispersive X-ray (SEM-EDX), and computed tomography X-ray (CT) imaging. Dissolution of plagioclase at this boundary is clearly evident. The migration of the core/rind boundary appears to depend in part upon the dissolution of plagioclase and resulting formation of secondary porosity at the interface.
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