From deserts and beaches to playgrounds, sand is a common sight. But you might not know that sand is also a useful resource. Sand is the second most-used resource in the world after water, the BBC reported. However, the UN said that sand is not limitless and that we might be running out of .

    Sand is made up of very small  (piece) of rock, soil and minerals(矿物质). It can take tens of thousands of years to form. But now we are using sand more (quick) than it is being formed. According to the BBC, we use about 15 billion tons of sand every year  build houses, roads and other things. People also put sand in the [si:] to make new islands. For example, the Palm islands are made up of three [lɑːdʒ] man-made islands in Dubai, United Arab Emirates. In 2010, they  (take) 94 million cubic meters of sand to build. If people keep(use) this much sand, it will run out in many places. For example, Vietnam may run out of construction sand by 2020, Live Science noted.

     [sins] people need so much sand, they are trying to mine(开采) more of it. But this is bad for the environment. Mining sand may  beaches to disappear and more floods to happen in places close to the sea. Also, this may affect the habitats (栖息地) of many plants and animals.