Hard; little affected by moistening.
The grains of a sedimentary rock may be cemented by mineral being deposited between them by percolating water over time. It is the strength of the cement rather than the grains that governs the hardness of many sedimentary rocks. Calcium carbonate (lime) and silica are two common 'cements'.
Indurated substances such as humus, calcium carbonate and the oxides of silicon, iron and aluminium can bind soil particles together in a hard brittle mass. This hardened state persists even when wet.