Igneous & metamorphic rock

Igneous and metamorphic rocks are those which have been emplaced in a molten state or substantially altered by the effects of heaat nd pressure. In the United Kingdom such rocks outcrop mainly in Scotland, Northern Ireland, Wales and the South West and Northern Regions of England. Other than a few small, usually heavily exploited, outcrops in the Midlands, the remaining parts of England are devoid of resources. Traditionally, igneous rock (including metamorphic rock) was used for building and ornamental stone, road setts, kerbs and pavements but these outlets are now minimal and the material is used preponderantly as crushed stone aggregate in road making with important minor applications as concrete aggregate and railway ballast. In 1975 estimated consumption of crushed rock natural aggregate in Great Britain (limestone, igneous rock and sandstone) was 110M tonnes of which 32M tonnes was contributed by igneous rock. Although normally of secondary quantitative importance as a general aggregate, igneous rock becomes of primary importance in areas where other materials such as limestone or gravel are not economically available. Certain types of igneous rock (and to a lesser extent some sandstones) are of prime importance in that they provide the main natural sources of skid-resistant material available for road surfacing in the United Kingdom. Igneous rock is often produced from quarries located in relatively small outcrops of preferred material and if these serve large markets, as is the case in Leicestershire or at some coastal sites, the quarries may be relatively large with outputs exceeding 0.5M tonnes per annum. Otherwise most important quarries tend to be of medium size with outputs in the range 0.1-0.25M tonnes per annum. The growth of the industry in recenty ears has led to environmental problems which are common to most aggregate producers. These include intrusion on the landscape, air and ground vibration caused by blasting, noise and dust from processing plant and difficulties in accommodating large volumes of mineral traffic on minor roads.