石头落水会下沉,这是常见的事,因为石头的比重比水要大得多。可是有一种石头,当投入水中时,它却会像鸭子一样地浮在水面上不沉,这就是人们所说的浮石,俗称蜂窝石或水浮石。浮石是一种火山岩石,以玄武岩质居多。它的内部结构松散,充满了大大小小的气孔,就像泡沫塑料。其孔隙度有 It is not uncommon for rocks to sink when the water falls, because the proportion of stones is much greater than that of water. However, there is a kind of stone which, when put into the water, floats like a duck and does not sink. It is what people call pumice, commonly known as honeycomb stone or pumice stone. Pumice is a volcanic rock, mostly basalt. Its internal structure is loose, full of large and small pores, like foam. Its porosity is