You may have heard of Bermuda's pink sand beaches, or of Hawaii's green and black sand beaches.Sand grains are formed when rock or other hard material is broken down by waves, a process that can take thousands of years. Beaches with pebbles or course sand are very young while beaches with fine sand are older. The color of sand grains comes from the original material that formed the sand. For example, white sand on tropical beaches is pulverized pieces of dead coral. (Coral skeleton is white because it is made of calcium carbonate, a mineral also found in chalk and human bones.) The green beach on the big island of Hawaii is green because the particular kind of rock that formed the sand (a type of cooled lava called basalt) has high amounts of a green mineral called olivine. Olivine is one of the most dense minerals in basalt, and so it hangs around long after the other, lighter minerals are eroded by waves and washed away. If you look closely at the sand on our own Santa Barbara beaches, you will see that it is made up of many different-colored grains and maybe even small pieces of shell. Look closely for some clear sand grains. Can you guess what type of rock makes these? (Hint: it's the same mineral found in many semi-precious gem stones, and you might find pieces of it while hiking in the mountains.)
Different rocks and minerals are what make up the sand. These little fragments of rock come from the mountains all around here, and are eroded and carried down to the beaches by rivers. The whitish fragments are quartz; the pinkish-beige fragments are most likely feldspar; the black bits are usually hornblende, and sometimes biotite mica. The colors of beach sand depends on the rocks that the sand comes from.