SAND is in high demand. In some parts of the world, people are going to increasingly great lengths to get their hands on the golden grains. A “sand mafia” in India intimidates locals in order to extract and transport the material. In Morocco and the Caribbean, thieves are stripping beaches bare. Even though fully accounting for illegally mined sand is not possible, sand is easily the most mined material in the world. According to the UN Environment Programme (UNEP), sand and gravel account for up to 85% of everything mined globally each year.

Modern cities are built with, and often on, sand. Most of it is used in the construction industry to make concrete and asphalt. No surprise, then, that Asia is the biggest consumer of sand. China alone accounts for half of the world’s demand. That reflects the country's breakneck pace of construction: the government reckons it built 32.3m houses and 4.5m kilometres (2.8m miles) of road between 2011 and 2014. Sand also has industrial uses: it is used to make glass, electronics, and to help extract oil in the fracking industry. And vast quantities of sand tend to be dumped into the sea to reclaim land: Singapore, for example, has expanded its land area by over 20% since the 1960s in this way. The Maldives and Kiribati have used sand to shore up their islands against rising sea levels. The UN forecasts that, by 2030, there will be over 40 “megacities” home to more than 10m inhabitants (up from 31 in 2016), which means more housing and infrastructure will need to be built. And sea levels will continue to rise. So sand will only become more sought after.

But why is there a shortage, when sand seems so abundant? Desert sand is too smooth, and so cannot be used for most commercial purposes. In any case, the proximity of sand to construction sites is generally important too: because sand is relatively cheap, it tends to be uneconomical to transport across long distances. Unless there are deep pockets involved: Singapore and Qatar are big importers, per citizen. Australian sand was transported to a faraway desert to build Dubai’s Burj Khalifa tower. Most countries also have rules in place about where, and how much, sand can be mined. But voracious demand has sparked a lucrative illegal trade in many rapidly developing countries. The result is that existing deposits are being mined more quickly than they can be naturally replenished, which is damaging the environment. Dredging causes pollution and harms local biodiversity. Thinning coastlines affect beaches’ capacity to absorb stormy weather.

Fortunately, there are substitutes for sand: asphalt and concrete can be recycled, houses can be built with straw and wood, and mud can be used for reclamation. In rich countries, government policy will encourage a shift towards such substitutes. According to Britain’s Mineral Products Association, for example, nearly a third of all housing material used in Britain in 2014 was recycled. Singapore is planning to rely on Dutch expertise for its next reclamation project, which relies on a system of dykes and is less dependent on sand. In poorer countries, too, builders are likely to shift away from sand as its price rises. But, unless law enforcement improves, that will be a very slow process.