A combination of rapid population growth and global urbanization is straining a crucial, often overlooked material: sand.

Why it matters: The explosive growth of cities around the world is driving an unprecedented demand for sand. The global rush to fill that demand has triggered a host of consequences, including environmental disasters and organized crime.

The big picture: We use 55 billion tons of sand every year, making it the third most used natural resource in the world. Without sand there is no asphalt, glass or concrete — the skeleton of the 21st century city.

Countries pour billions of tons of concrete every year as cities around the world grow.

The catch: Concrete requires a specific type of sand found on the floors of rivers, lakes, beaches and floodplains.

Desert sand is useless for concrete, and cities such as Dubai, which sits on the Arabian Desert, have had to import construction-grade sand.

The impact: The effects of unlimited extraction on the environment can be severe. Researchers have found that river dredging in India has contributed to flooding in Kerala. China banned sand-dredging on the Yangtze River in 2000 after bridges were undermined and thousands of feet of riverbank collapsed.

Sand dredging in Lake Poyang — China's largest body of freshwater — has disrupted bird migration patterns, destroyed fishing areas and increased the lake's vulnerability to drought.

Sand mining in the San Jacinto River may have also contributed to Hurricane Harvey's disastrous flooding of Houston in 2017.

In some countries, illicit mining operations routinely violate sand excavation regulations to fuel a growing black market. "Sand mafias" in India have killed journalists and police who have tried to stop them.

Vince Beiser writes in the New York Times that growing cities may have to truck sand in from elsewhere if local sources disappear. This could drive up the price of pouring concrete specifically and construction generally because it is costly and difficult to transport. One cubic foot can weigh up to 100 pounds.

What to watch: Engineers are testing materials like recycled plastic, bamboo, wood and straw to replace sand in cement, and it's possible to recycle sand from demolition waste.

Thilo Juchem, the president of the European Aggregates Association, told Axios that recycled and alternative materials can not replace the demand for billions of tons of sand.

"Trying to find ways to use raw materials more efficiently and wisely could ease the pressure on the demand or consumption side, but most likely only marginally," Juchem said.

The bottom line: Sand mining regulations could alleviate some of the effects of extraction, depending on the government's ability to enforce them, Beiser writes.

Go deeper: