This beach sand is derived from stream and marine erosion. Under the microscope, you can better see barnacles shards, bivalve shell fragments, and flecks of porphyritic basalt. When a storm batters a beach, for instance, harder, heavier minerals—like magnetite and muscovite—can rise in the sand column, and temporarily change the color of the beach.
This shift in sand color can make it possible to see storm events even three or four years later. As the remaining cinder cone erodes, it deposits the green shiny, translucent crystals, known as olivine , which gives the beach its moss-green luster.
Sample from Lizzie Reinthal. Credit: Mark A. Coastlines can also be riddled with remnants of dead marine organisms, such as the White Cliffs of Dover on the southeastern coast of England. In , a study published in Global Biogeochemical Cycles found evidence that single-celled marine algae, called coccolithophores, played a key role in creating this formation.
When coccolithophores die, their hard calcite plates sink and build up into chalk on the ocean floor. Scientists say that a great algal bloom in the Southern Ocean almost million years ago is the likely source of the chalk composites of the White Cliffs of Dover. Around the s, the rise in population and urban development accelerated our extraction of sand and gravel. Today, sand is not only an ingredient in buildings and streets, but is used to make glass, paint, and microchips in smartphones and laptops.
What creates those different colors? Why is some sand soft and fine, but other types feel rough? Where does beach sand come from, anyway? The sand found on a specific beach is created by its surroundings.
Most beaches get their sand from rocks on land. Over time, rain, ice, wind, heat, cold, and even plants and animals break rock into smaller pieces. This weathering may begin with large boulders that break into smaller rocks. Water running through cracks erodes the rock. This forces the cracks open wider. The freeze-thaw cycle happens over and over again. Each time, gaps widen. Pieces break off.
Over thousands of years they break down into smaller and smaller rocks, pebbles, and grains of sand. Pounding waves and the ebb and flow of tides also make sand. These motions knock rocks, pebbles, and sand grains against each other. This action wears them down. It also smooths the rough edges. The smaller and rounder the grains become, the softer the sand feels. Different minerals in rock weather differently.
Others, such as quartz and feldspar, are much tougher. These two minerals last longer than others and make up a typical sandy beach. Quartz tinted with iron oxide appears light brown. Feldspar is tan. Together, they create the sand-colored hue of many beaches.
In areas with volcanoes, sand comes from volcanic rock. This explains the colored beaches of the Hawaiian Islands. Green beaches have lots of the mineral olivine. And black beaches are created from obsidian, or volcanic glass. When lava flows into water, it hardens so quickly it shatters, creating shards of obsidian. Over time, waves smooth the shards, turning them into sand. Beach sand is more than just minerals from land, however. Some sand also comes from the ocean.
Shells and other hard pieces from marine organisms wash up on shore. Pounding waves break them into smaller, sand-sized pieces. In tropical areas with coral reefs, this is the main source of beach sand.
Such reefs are home to animals, like parrotfish, that graze on coral. Parrotfish eat the algae that live on and in the corals. They chow down on big bites of coral, including the skeleton. Chunks of skeleton get ground up and pooped out as sand. A single parrotfish can create hundreds of pounds of sand each year! Email your Friend. Submit Cancel. September 15, Thanks for the good times! Here's Where To Find Shelter. August 09, What are coral atolls made of?
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