Abstract:
In hard rocks are included all those geological formations the drillability of which is low and the intergranular porosity is practically absent e.g. igneous and metamorphic rocks as well as limestones, dolomites and highly cemented sandstones, The definition used in the UN-family for hard rocks is "Compact, non-carbonate, non-volcanic rocks". However, as secondary porosity due to fracturing and solution activity is the main controlling factor for the occurrence of ground water in carbonate and volcanic rocks also these rocks types have been included under the hard rocks.
