Short answers, pulled from the story.
Sand is a granular material composed of finely divided mineral particles, most commonly silica in the form of quartz in inland and non-tropical coastal settings. The second most common type is calcium carbonate, including aragonite built by coral and shellfish, and some sand is calcium sulfate such as the gypsum at White Sands National Park.
Geologists define sand grains as ranging from 0.0625 millimeters to 2 millimeters in diameter, while the Unified Soil Classification System used in engineering and geology defines sand as particles between 0.074 and 4.75 millimeters. Grains larger than sand are gravel, and grains smaller are silt.
Desert sand is unsuitable for construction because its grains are rounded and smoothed by being blown in the wind, so they do not lock together to form solid concrete. Rough sand from the sea and angular river sand bind far better, which is why they are in high demand.
Sand forms as rocks erode and weather over long periods, mainly by water and wind, breaking into ever smaller grains. Granite is the most common rock to form sand, because its feldspar minerals dissolve faster than quartz, and sand made by weathering is called epiclastic.
Sand is a non-renewable resource over human timescales, and demand for sand suitable for concrete has grown with cities and construction. A 2022 United Nations Environment Programme report stated that 50 billion tons of sand and gravel are used every year, and global demand in 2017 reached 9.55 billion tons as part of a 99.5 billion dollar industry.
Sand is used in concrete, glass, bricks, mortar, and the production of silicon, as well as in water filtration, sandblasting, hydraulic fracturing, and sandbags. It also serves agriculture, aquariums, rail and road traction, beach nourishment, and recreation such as sand castles and sandboxes.
Dubai imported sand from Australia because the sand needed to build its infrastructure and the Dubai Islands exceeded local supplies. The artificial islands required more than 835 million tonnes of sand at a cost greater than 26 billion US dollars.