ABSTRACT
This chapter provides the geologist with suggested field observations that will aid in identifying relationships between the geologic properties of rocks and sand and gravel and their likely performance as an aggregate. Naturally-occurring aggregate deposits, whether sand and gravel or source rock for crushed stone, are formed by a variety of geologic processes. Crushed stone is classified according to the type of rock from which it was produced: Sedimentary, igneous, and metamorphic. The largest single use of natural aggregates is in construction, and much of that aggregate is used in portland-cement concrete or bituminous mixes. Sand and gravel deposits are accumulations of durable rock fragments and mineral particles. The preparation of a map showing the distribution of potential aggregate sources is essential for resource assessments. Existing geologic maps serve as an excellent source of information for determining the location of potential sources of aggregate. For most regional assessments, the quantity estimates of aggregate resources should be considered inferred reserves.
