2. Occurrences and associations of sources

Abstract

This section is intended primarily as an introduction and guide for non-geologists engaged in the aggregates industry. It is intended to be useful in understanding the more straightforward day-to-day geological situations that arise in the development and management of workings. It provides a basis for recognizing the more complex and intractable problems for which specialist geological advice is likely to be needed.A main contribution of geologists to the study of aggregates is the recognition that rock material owes its properties to its origin, its mineral composition and to the geological processes that have affected it through time. Knowledge of the qualities that determine the suitability of a rock (or concentration of rock fragments) for use as aggregate enables the prospecting geologist to make an informed search for new deposits, recognizing and defining the clear, though not always simple, relationships that exist between the composition, texture, grain-size, fabric and state of weathering of a rock and its likely performance as an aggregate in an engineering structure or other application.Rock is natural material that forms the crust of the parth. Some rocks are relatively soft, that is to say, weak and easily deformable. Others are hard, strong and durable. Rock so defined includes the ‘soil’ of engineers (that is, all unconsolidated deposits overlying bedrock). However, it does not cover the soils of pedologists (the earthy materials forming the ground in which land plants can grow). Rocks may be examined in cliffs and quarries at the surface and in mines and boreholes.