claysurrounded

Claysurrounded is a term used in soils science and sedimentology to describe a textural feature in which clay minerals form a continuous coating around a particle, pore space, or fragment. The resulting rind creates a distinct clay-encased unit within the rock or soil. The coating is commonly composed of illite, kaolinite, smectite, or mixed-layer clays, reflecting the local clay-mineralogy and diagenetic history.

Formation: Claysurrounded develops during diagenesis and pedogenesis when clay minerals precipitate from pore waters or adsorb onto available surfaces, creating a net surrounding film. Conditions such as gradual cementation, changes in salinity and pH, and ionic exchange promote coherent clay rims around grains, shells, or silica grains.

Physical implications: The clay rind reduces pore throat size around the coated object, altering porosity and permeability locally. It can enhance sorption of organic molecules and metals, influence diffusive transport, and potentially help preserve organic matter by limiting water movement into the grain boundary.

Detection and occurrence: Claysurrounded is identified in thin-section petrography and scanning electron microscopy as a continuous clay boundary enveloping a grain. X-ray diffraction can indicate the presence of clay minerals in the boundary; image analysis may measure rind thickness and coverage. It is observed in both sedimentary rocks and clay-rich soils, especially in systems with fluctuating redox or hydration states.

Significance: The feature matters for hydrocarbon reservoirs, groundwater flow, and biogeochemical cycles because it modifies flow paths and reactive surface area. It is studied to understand diagenetic histories and sedimentary textures, and it is sometimes referred to as a clay-encasement or clay-bound grain in the literature.