ABSTRACT
The term ‘hard rock’ is used, in general, for all geological formations which are compact and massive and do not possess any primary porosity. Hard rock is also known as fractured rock. According to Larsson (1984) all kinds of igneous and metamorphic rocks are considered as hard rocks, excluding volcanic and carbonate rocks which may have primary porosity. The generalized definition of hard rock stressing its hydrogeological character as given by Gustafsson (1993) is that hard rock “includes all rocks without sufficient primary porosity and (hydraulic) conductivity for feasible groundwater extraction’’. Accordingly, Archaean and Precambrian sedimentaries, carbonate rocks and younger volcanics possessing similar hydrogeological character can also be considered as hard rock. Hard rocks cover large areas in several parts of the world. There are shield areas like Canadian, Guianan and Amazonian, Baltic, African, Indian, Australian, Angaran (Siberian) and Antarctic where hard rocks are widely exposed. The other significant exposures of hard rock are Armorican Massif, Spanish Meseta, Massif Central in France and Bohemian Massif. The total area of shield-rock outcrop is about 30 million sq. km covering around 20 percent of the land surface (Gustafson and Krasny, 1993; Krasny and Sharp, 2007). In this book the hard rocks, viz., granite, gneiss, schist, phyllite, quartzite, basalt etc. excluding carbonate rock are discussed. However, in the following chapters while explaining the geophysical methods some carbonate rock case studies are given. The methods described can be used appropriately in carbonate rocks also.
