Some rocks from volcanoes break down to form black sand.
有些火山岩被撞碎后会形成黑色的沙。
2
When these rocks break down into the grains that make up the sand on our beaches, their colour is mostly determined by the presence or absence of iron.
当岩石分解成为颗粒够成沙滩时，颜色则是由铁元素氧化物的存在与否决定的。
3
They tried to break the icy sand with their knives, but it was not easy.