Sand is an incredibly common form of micro-stone and mineral particles. Sand is found all over the world, in hot and cold climates, and the bulk of sand is found in deserts and on beaches. The commonality of sand by beaches is a result of wave activity, where stones are moved back and forth and so cannot sit still and fuse with each other; the stones wear down to small forms that are clean of organic deposits, creating lines of sand across beaches. Sand is differentiated from dirt in that the organic and bacteriological components of sand are very minor compared to dirt, which is thicker and connected by its organic components.
Sand has a wide variety of industrial uses, including construction, fill, abrasion (seen in gem-polishing and sandblasting) and agriculture. Despite sand's low organic component, it is very useful for drainage and moisture control. Sand is used to refill beaches after strong climate activity, to prevent erosion of shorelines. Of course, the most important use of sand historically is to make glass; sand (composed mostly of silica) is melted at high temperatures and then poured or blown to create clear glass with many different uses. Because of its density, sand is used in sandbags to prevent weather damage and in fortifications; sand is also useful in roads, concrete, and water filtration (natural filtration of water through sand forms the basis of fresh, non-toxic groundwater and aquifers).
Sand is found abundantly in nature, mainly in river beds but it is also available in layers of earth and can be taken out by pit mining. Sand is graded by its grain size, the courser is stronger. Clay is found in sand as impurity and makes it unsuitable for building industry.
Building industry makes use of cement-sand mortar for masonary work in ratios 1:4 to 1:8. The cement sand mortar is also used for plastering.
Other use of sand is building industry is in plain reinforced concrete. Concrete is a cement-sand-gravel mixture generally in ratio 1:2:4 but other ratios are also used depending on the strength requirements. Concrete is used for not only making precast structures like building blocks, beams, and slabs (the latter are reinforced with steel) but also for flooring, roofs, beams and bridges cast at site. Canals and water courses are also lined with concrete with used precast structures (outlets etc). Concrete is also used for road construction where heavy machinery is to be moved e.g. runways.
So wherever we use cement sand mortar or concrete, we use sand as essential ingredient.