sands

Sands are granular materials composed of rock and mineral particles, typically 0.0625 to 2 mm in diameter. The most abundant constituent is silica in the form of quartz, but sands may also contain feldspar, mica, and heavy minerals. Colors vary with composition and weathering, from pale quartz sands to iron-rich yellows and reds, to dark accumulations of magnetite or volcanic glass. They occur in deserts, beaches, rivers, and dunes.

Formation and distribution: Sands form by weathering and erosion of rocks, with particles transported by wind, water, or ice before deposition in deserts, beaches, rivers, deltas, and continental shelves. Transport influences sorting and rounding: wind-blown sands are often well sorted and rounded; river sands may be more angular and poorly sorted.

Properties and composition: Sand grain size is typically described as very fine to coarse and is often classified by sieve sizes. The mineral content ranges from predominantly quartz to mixtures including feldspars and heavy minerals. Porosity and permeability vary with grain size and sorting, influencing drainage and groundwater flow.

Uses: Sand is a major component of concrete and mortar, and silica-rich sands are essential for glassmaking and foundry work. It also serves in filtration, landscaping, and beach or recreation contexts. The suitability of sand for a given use depends on grain size, hardness, and purity.

Environmental and economic considerations: Sand is a globally traded resource. Mining can cause habitat destruction, coastal and riverbank erosion, and water table impacts. Sustainable management includes regulation, responsible extraction, and restoration of dunes and shorelines.