shellsand

Shellsand is a sedimentary material composed predominantly of the fragments of shells and other calcareous debris. It forms in coastal and shallow marine settings where shells are produced, accumulate, and become lithified or remain as unconsolidated sand. The material is rich in calcium carbonate and often contains a mix of mollusk, brachiopod, coral, and foraminiferal remnants. Shellsand deposits are common on beaches, tidal flats, lagoons, and nearshore offshore areas, and they may also occur as ancient shell beds preserved in the rock record.

Physically, shellsand often has a lighter color and a distinctive texture due to recognizable shell fragments. Grain sizes range from fine to coarse sand, and the material can exhibit variable porosity depending on the proportion and condition of the shell fragments. In diagenesis, shell fragments can dissolve and reprecipitate cement, potentially forming coquina-type limestones under suitable conditions.

Uses and significance vary by region. In some areas, shellsand is quarried for crushed calcium carbonate used in lime production, cement, soil amendment, or as a decorative aggregate in landscaping. Shell-rich sediments can also provide paleontological and archaeological information when found in the sedimentary record or as shell middens. Environmentally, shellsand habitats can be sensitive to erosion, dredging, and habitat disturbance, with potential impacts on coastal processes and marine life if extraction occurs.