1. A rigid, wave-resistant build-up constructed by carbonate organisms. Types of reef include patch reefs (small and circular in shape); pinnacle reefs (conical in form); barrier reefs (separated from the coast by a lagoon); fringing reefs (attached to a coast); and atolls (isolated reefs enclosing lagoons). Factors influencing reef growth include: (a) water temperature (optimum 25 °C); (b) water depth (must be less than 10 m); (c) salinity (normal marine salinity is necessary); (d) wave action (intense wave action favours coral growth); and (e) turbidity (coral growth requires clear water and an absence of terrigenous suspended sediment). The diversity of species found in a reef will be a function of salinity and water temperature, with stressful conditions resulting in a reduction of species present.

2. In mining, certain palaeoplacer gold deposits in Australia and South Africa.