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 coarse 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.)

The colors are from the different rocks and minerals that 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. In Hawaii you can find black sand beaches, because the sand comes from eroded basalt - lava from the volcanoes. On the southern-most tip of Hawaii there is a green-sand beach. That sand is made of olivine, an igneous rock that is rare on the surface of the earth because it breaks down up here, and is stable inside the earth (where the pressure is higher and the temperature hotter.) I have seen this olivine beach - it is very beautiful!

I have also been on black-sand beaches in Alaska, where the sand comes from eroded basalt from the volcanoes.

Remember , sand is simply the product the erosion of the rocks rubbing each other under the action of the waves. So if the bottom of the ocean is made of black lava (as in Hawaii) you will have a good chance if the beach is an old beach that it will have a lot of black sand coming from the rubbing the lava rocks or sea shells under the action of the surf and the waves. The sea shell also can be at the origin of a beach color. Sea shell are usually white and the million of small shell pieces coming from the erosion will give the beach its color. I hope this answer satisfies some of your curiosity.

Beach sand has different colors because there are many different minerals that make up sand. In California, our sand usually looks white because it has minerals like quartz and pieces of shells that are made of calcium carbonate.