Patrick O'connor, Age 7, Of Peterborough, Ont., Canada, for his question:     

The crisp, clean, witty sand on the beaches is one of the greatest treats in the world. We can thank the pounding waves for it. We can also thank the rocky crust of the earth and its fiery volcanoes.

Most beach sand came from granite which was poured from volcanoes in rivers of molten lava. Granites are mixtures of different minerals. Several of these rocks are peppered with gritty grains of quartz  which is the hardest of the common stones. The pounding waves of the sea bash granites to powder and wash away the pieces. But the mains of quartz are too hard. They are left behind to collect on the beach in gritty layers of golden sand.