Moisture Capacity of Rocks

the capacity of rocks to absorb and hold a given volume of moisture, expressed in percentage relative to completely dry rock.

The moisture capacity is characterized by a coefficient of saturation expressed in percentages of weight (the relation-ship of the mass of water to the mass of the dry rock) or of volume (the relationship of the volume of water to the volume of rock). Rocks are divided into saturable types (peat, silt, loam, and clay), slightly saturable types (chalk, marl, clayey sand, and loess), and nonsaturable types (monolithic igneous and sedimentary rocks).

The moisture capacity of rocks can be maximally molecular, with maximum quantities of hygroscopic (strongly bonded) and pellicular (friable on two planes) water preserved by the rock; capillary, with water held in capillaries or around rock particles under the influence of molecular forces; complete, with water held by completely saturated rock; and maximally hygroscopic, with maximum quantities of water absorbed by the rock from the air with a release of heat corresponding to the maximum quantity of firmly bonded water formed in the soil.