Beyond Sea Glass and Shells
By Jan Whitted
Black sand beach in Iceland (DarknessAsylum/Shutterstock.com).
When you comb the beach, what treasures are you looking for? Maybe you collect beautiful sea glass, gather intact shells, save well-worn pottery shards, or can’t resist a perfectly smooth stone. But these special objects live alongside another treasure—the sand itself.
Sand collectors (arenophiles) gather sands from around the world and prize the differences in color and texture on every beach. What’s behind these differences? How can you know what the beach you’re walking on today is made of?
Sand grains under a microscope (Barou Abdennaser/Shutterstock.com).
You may have heard that sand is made up of quartz crystals—70% of the Earth’s sand is quartz—but sand doesn’t need to have any quartz in it at all. Sand is defined by its size rather than its composition. Sand is sand if it has particles small enough to be carried by wind and water and large enough to settle to the earth (a range of 1/8 millimeter to 2 millimeters). Smaller particles are dust, and larger particles are gravel.
Those tiny, settled particles—both visible to the naked eye and particles too small to be seen without a magnifier—determine the color of the sand. What has broken down to become the sand you’re walking on? A mountain? Rock from a copper or coal mine? Sea urchins or barnacles?
Seeing what’s in the sand requires a high-powered microscope. In 1990, scientist and photographer Gary Greenberg invented the Edge 3D microscope that magnifies sand 40X to 400X. His books, A Grain of Sand: Nature’s Secret Wonder and The Secrets of Sand (with Carol Kiely and Kate Clover), along with his website www.sandgrains.com chronicle the amazing variety of tiny treasures at our feet.
On a typical beach you could be looking at feldspar, the most common mineral on the planet, along with bits of quartz that have turned brown from exposure to iron oxide. But if you look closely at the sand, it is so much more than little brown rocks!
Left to right: Sand containing gemstones and other minerals. (Knorre/Shutterstock.com). Sand from Barbuda Island made of tiny pink shells (BlueOrange Studio/ Shutterstock.com). Green sand from a Hawaiian beach (Filippo Nenna/Shutterstock.com). Purple and red sea urchins eating a piece of kelp (Brandon B/Shutterstock.com).
Red and pink sand can come from eroded sandstone, iron-rich agates, and from rocks that started out near copper mines. Tiny forams, single-cell marine creatures that live in the coral reef, often give sand its color. But sand can also contain gemstones: tiny garnets that get left behind because they are denser than other particles found in volcanic rock.
Green sand contains olivine (and its rare-gem version, peridot), a mineral brought to the Earth’s surface by volcanic eruptions, which is why there are green beaches in Hawaii, Norway, Guam, and the Galapagos Islands. Remnants of marine life, like sea urchin spines, may also be green, as are the minerals diopside and epidote. Green nephrite jade, although rare, can be found at Big Sur in California as well as in British Colombia.
Pfeiffer Beach in Caliornia with purple sand (Iuiia K/Shutterstock.com).
Blue and purple sand can get their color from sea urchin spines and mussel shells. The mineral diopside can also be blue, and pink quartz mixed with a darker mineral can appear to be purple. Tiny animal skeletons, like sea urchin spines and bryozoa, a simple animal that lives in colonies in the ocean, lend a rainbow of colors to sand.
Star-shaped sand, the shells of a microscopic organism from Japan. (koi88/Shutterstock.com).
When you find a white sand beach, it could be made of pure quartz crystals originating from granite mountains. For example, the Appalachian Mountains feed the white sands at Hilton Head, South Carolina, and in the Gulf of Mexico. But it’s possible that a white beach contains no quartz at all. Island beaches are made up of the shells of marine organisms, like sea urchins, algae from coral reefs, sponges, bivalves, and forams, turned even whiter as they are bleached by the sun.
Ooids from a beach on The Joulter Cays, The Bahamas (Mark A. Wilson). Coral sand from Molokai, Hawaii (www.sandatlas.org/Shutterstock.com).
In Bermuda, the white can be from ooids, layers of calcium carbonate that form around microscopic fragments of minerals or shrimp pellets and have been made round and smooth by the strong tides. And some lakeshores and inland dunes are made of pure white salt and gypsum.
Black sand comes mainly from volcanic rock, but you may see other black elements, like fossilized shark teeth or bits of coal (Northern England), and perhaps mica and other iron minerals (Norway).
Next time you go to the beach, consider packing a pocket magnifier that’s at least 10X (100X if you can), and take a closer look at the colors in the sand you’re walking on. But even if you prefer to fill your pockets with beach finds rather than scientific tools, you’ll know there’s an entire, marvelously varied, and colorful hidden universe beneath your feet.
Learn more arenophiles and sand collecting.
Learn about sands from around the world, what makes up different sand types, and the arenophiles and artists who collect sands and use it in their art. Articles›
View macro and micro views of Dania Beach, Florida in this short video
Learn more about beach rocks.
Learn more about beach rocks including agates, Cape May diamonds, Yooperlites, fulgurite, puddingstone, and more. Articles ›
This article appeared in Beachcombing Magazine Volume 43 July/August 2024.
