near Index, Snohomish County, Washington, USA |
CaCO3 - Occurs as main mineral component within concretions. Calcite is the cementing agent, filling the pore space in clay and sand sediment layers. Diagenetic calcite precipitation in sediment pore space produces light-gray, flat, rounded nodules that weather out of the hillside. Fine-grained clay-rich concretions are commonly symmetrical. Sand-rich concretions are typically irregular in shape. Concretions up to 15 cm occur in outcrop or loose, eroded from the clay bank. |
Clay-rich concretion cemented with CALCITE |
Clay-rich concretion cemented with CALCITE |
Sandy concretions cemented with CALCITE |