HUMIDITY of the rocks (EN: humidity of rocks, moisture content of rocks; DE: Bergfeuchte, Wassergehalt der Gesteine; FR: humidite des roches, teneur en eau des roches; ES: humedad de las rocas; RU: влажность) is the degree of the saturation with the water (of the film, capillary, and gravitational types) of the pores, cracks, and other voids of the rocks under the natural conditions.

They distinguish the massive humidity, namely, the ratio of the mass of the water, which is contained within the sample, to the mass of this sample after the drying; the voluminous humidity, namely, the ratio of the volume of the water within the sample to the volume of the sample; the normalized humidity, namely, the ratio of the volume of the water within the sample of the rock to the volume of the skeleton of this rock; the relative humidity, namely, the ratio of the volume of the water within the sample to the volume of the pores within this sample.

The humidity under the laboratory conditions is determined using the weighting method (the drying of the rock at the temperature of 105-110 degrees Celsius, and the subsequent weighting of this rock), and the humidity within the massif of the rocks is determined using the methods, which are based on the determining of the dependence of various physical properties of the rock (the thermal conductivity, electric conductivity, and others) on the humidity of this rock. There possess the greatest ability to be saturated with the moisture the peat, brown coal, tuff, clay, and loess. The value of the humidity fluctuates significantly because of the hydrogeological situation, and may range from several percents up to 40-50% or more within the limits of the single deposit. Depending on the mineral and particle size composition of the rocks, on the sizes and shapes of the particles, the ratio of the amounts of the different types of the water within the rocks may be different. For example, the sands contain mostly the gravitational water; the clays, loesses, and loams contain mostly the molecular and capillary water. The content of the molecular water is approximately 0.2% within the quartz sands, 5% within the loesses, and 10-30% within the clays. The content of different water within the rocks determines the water yield of these rocks.

the humidity is the most important characteristic of the rocks and useful minerals. The humidification of the rocks modifies practically all physical properties of these rocks, when the water, as the constituent part of the rock, increases the electric conductivity, heat capacity, and thermal conductivity of the rock, or acts as the physical-chemical medium, which is impacting onto the mineral phase, thus causing the dissolution of the rock, the soaking, the decreasing of the strength, the increasing of the plasticity. The increased humidity within the massifs of the rocks leads to the deformation and destruction of the sides of the open-pit mines, and of the mine workings.

The humidity is taken into account during the calculation and design of the systems for the water drying, for the injection of the water into the layers of the coal, of the energy capacity for the processes of the drying of the ores before the roasting, within the calculations for the various stages of the beneficiation, and so on. The humidity of many useful minerals (for example, of the coal, peat, petroleum, and natural gas) is one of the indicators of their quality, and is regulated using the GOST governmental standards.