The geologist concerned with aggregate should be aware that under the term aggregate there is a very broad range of geological materials. In the foreword to Dolar-Mantuani (1983) we wrote:
Every kind of rock and every mineral species that occurs on this planet as a solid particle, grain, or mass—except ice—is potentially subject to evaluation for use as concrete aggregate. Therefore there is no kind of rock and no mineral species that is not of potential interest to the petro-grapher working on concrete aggregates. However those substances that can significantly affect the performance of concrete for better or worse when they occur as aggregate constituents are more important and, among these, those that occur most frequently are of greater interest.
Any bit of solid material used as an inclusion in a matrix or binder in a composite construction material is considered to be aggregate if it remains solid at the temperature of use and does not dissolve in the environment of use, so long as it is used as particulate material. As noted in the quotation, ice is not evaluated as aggregate for concrete, but ice could be used as aggregate in an appropriately low-temperature environment. Rock salt— halite (NaCl)—which would dissolve in many environments, is for that reason, among others, rarely used as an aggregate, yet rock salt has been quite successfully used as fine and coarse aggregate with portland cement, and with a saturated NaCl solution used as mixing water, to make concrete to plug a tunnel in a salt mine (Polatty and others, 1961).