Splendid Sands

pink sand under a microscope

Leo Kenney and Kate Clover have been collecting sands from around the world for years. Their travels take them across the United States from Oregon to Florida, from Massachusetts to California, and from the Great Lakes to the Gulf Coast. They have both beachcombed extensively around the world, but their international sand collecting is now usually through trades with other collectors, who gather sands on beaches and in deserts as they travel. Kate lives in Minnesota and loves mineral sands full of garnets, magnetite, and sapphires, as well as biogenic sands with sea urchin spines, barnacle plates, mollusks, sponge spicules, and forams, visible under a microscope. Leo stores his collection of about 5,000 samples in his home in Massachusetts, where he enjoys photographing his favorites. Following are some of the rainbow-colored sands they have collected over the years.

Mercury Bay, Coromandel Peninsula, New Zealand. The rugged Coromandel Peninsula on New Zealand’s North Island is renowned for both shorelines and forests. Jutting north, the peninsula separates the Hauraki Gulf and Firth of Thames in the west from the Pacific to the east. Mercury or Red Bay is a large V-shaped bay on Coromandel’s eastern coast. It was named in 1769 by English navigator Captain James Cook when he landed to make an astronomical observation of a Transit of Mercury.

The striking color of this sand comes from the polished fragments of a New Zealand endemic species, the pink barnacle Notomegabalanus decorus. This large species, which reaches up to three inches at the base is the most characteristic and well-known barnacle of the New Zealand Shelf and is found only in New Zealand waters. Other biogenic grains in this sand include tiny gastropods (snails), as well as remains of sea urchin spines (the striated green rods), coralline algae (the smooth white rods), and bivalves (like clams).

red and blue beach sand

Plage des Dunes, Bretignolles-sur-Mer, Vendée, Pays de la Loire, France. The seaside resort town of Bretignolles-sur-Mer lies along the southernmost coast of Brittany on France’s Atlantic shoreline. These beautiful sand grains are gemstones, and they congregate in waves and swaths on the beach. Winnowed by wave and tidal action, they segregate out from the quartz grains because they are “heavy minerals,” minerals with a higher density than quartz.

The sand is sprinkled with sparking blue sapphires, the aluminum oxide mineral corundum. Some pink and red grains are ruby, red corundum; others are garnet, a mineral that can vary in color. Some black grains are magnetite; others are likely spinel, both iron-bearing minerals. The green grain, near center, is epidote; the yellowish grains with the near 90° corners are K-feldspar. Adding to the sparkle in this sample is clear quartz.

Well-rounded and polished, this characteristic of sand grains is indicative of a high-energy coastline where waves perpetually pound the shore. And the sand grains, in non-stop motion, rub, round, and polish each other.

pink and yellow garnet sand under a microscope

Pictured Rocks Lakeshore, Lake Superior, Munising, Michigan. Tiny pink to reddish garnets are commonly found in sands. On the beach, swaths or layers of dark sands, perhaps with a pink to purplish hue, often include garnets.

Garnets are a group of silicate minerals that occur in many colors ranging from deep red to pink and purple to orange, green, and yellow. The pink to reddish varieties are the most common. All species of garnets share a similar crystal structure, but differences in chemical compositions determine the color. Individual grains often are round, an artifact of their original 12-sided, dodecahedron crystal shape; broken grains show conchoidal fracture.

Because of their hardness and density, garnets are considered a “heavy mineral,” and they are commonly found in beach sands along with other heavy minerals including magnetite, ilmenite, zircons, and even gold. They are a common rock-forming mineral in igneous, metamorphic, and sedimentary rock types.

microscopic view of yellow beach sand

Westcott Beach, Henderson, New York. Henderson is located on the eastern shore of Lake Ontario. The sand contains grains of clear and cloudy quartz, as well as yellow/orange feldspar grains.

Sand with this composition reflects rocks with similar mineralogy: granite and gneiss—both of which make up the ancient rocks of the Canadian Shield. Today, these rocks can be found on the rugged north shore of the St. Lawrence below Quebec and in the Thousand Islands area of northwestern New York state.

Granite and gneiss rock appear hard; but over eons, the coarse-grained rock breaks down as weathering processes attack the stone. As that happens, only the hardest mineral grains, the quartz and feldspar, survive. Ultimately, these sand grains were reworked and deposited as the glaciers retreated about 12,000 years ago.

macro view of green sand beach hawaii

Green Sand Beach (Papako¯ lea), South Point, Hawai‘i. South Point on the Big Island of Hawai‘i is the source of this green sand. These translucent green grains are olivine crystals. Near the ocean’s edge, olivine erodes from a nearby lava flow and concentrates on the beach by wind and surf action. Olivine, heavier than most other sand grains, remains behind when other grains are washed away by wave action. Olivine ranges from olive green to pale-yellow green depending on the proportions of iron and magnesium in its chemistry.

Pure olivine sand beaches are rare, but other Hawai‘i sands do contain some olivine grains. Beyond Hawai‘i, olivine is found in igneous volcanic rocks that are associated with divergent plate boundaries or oceanic hot spots. We see it in sands from volcanic islands like the Galapagos, Canary Islands, Guam, some Alaska islands, Ascension Island near the Mid-Atlantic Ridge, and elsewhere. Olivine is susceptible to weathering and is not found in well-weathered sands. If olivine is found in a sand, that location has a volcanic past.

dark green beach sand under microscope

Les falaises des Vaches Noires, Auberville, Calvados, France. Located on France’s northwestern coast, in the Normandy region, Les Falaises des Vaches Noires (the Cliffs of the Black Cows) got their name from sailors who saw the algae-covered rocks along the shore and thought they were cows grazing on the beach. Rather, they are blocks of soft Cretaceous chalk that eroded from the seaside cliff. Under the chalk lies Jurassic marl that is prone to landslides. Both rock formations are famous for the Jurassic and Cretaceous age fossils: ammonites, sea urchins, belemnites, shark teeth, corals, plus plenty of gastropods and bivalves.

Also on the cliff is a rich deposit of glauconite, the dark green grains in this sample. This iron mineral formed on the seafloor in a oxygen-starved environment (otherwise it would be red); today it is found below the chalk layer. It erodes from the cliffs and accumulates on the beach along with fragments of the chalk, and in this sample, a triangular shell fragment.

microscope view of blue and purple beach sand

Trinity Bay, Dildo, Newfoundland, Canada. The landscape of Newfoundland illustrates remarkable geologic history formed over many million of years by continental collision, mountain building, volcanoes, oceans, rivers, and ice sheets. It has some of the oldest rocks in the world.

Trinity Bay, located in the eastern zone, is a fragment of Gondwana, once part of southwestern Europe or North Africa that remained attached to Laurentia when the Atlantic formed about 200 million years ago. During the last ice age, ice sheets advanced and retreated many times and smoothed and polished wide areas and carved deep valleys through mountains. Along the coast, these valleys were later flooded by the sea, creating deep fjords.

The grains seen here include shales, the gray to green-black laminated grains as well as the red and purple ones. The yellow grains are sandstone. The speckled grain (center) is porphyritic andesite, a volcanic rock. The cloudy white grains are quartzite.

blue beach sand from mussel shells under microscope

Dead Horse Beach, Salem, Massachusetts. The name Dead Horse Beach goes back to the 1850s when this site was far enough from town to be a good place to bury dead horses; today, it’s popular with beachgoers.

Weathered shards of blue mussels (Mytilus) give this sand its unusual texture and blue and white colors. The flattened profile of these grains reflects the shell’s sheet-like inner construction.

Blue mussels are common in the coastal waters of the North and Mid-Atlantic. They feed by filtering organic particles (mostly phytoplankton) from the water column. Mussels are an important prey item for lobsters, crabs, whelks, gulls, and diving ducks and a popular seafood item on menus today.

A green sea urchin spine fragment sits just below center. Sprinkled throughout are mineral grains of eroded granite.

macro view of black beach sand from hawaii

Kings Pillars, Cape Kumukahi, Big Island of Hawai’i. Cape Kumukahi is located on the easternmost point of land on the Big Island of Hawai‘i, east of the town of P¯ahoa. The rocky cape is on the end of Kilauea’s East Rift Zone where lava from the volcano last flowed downslope and into the sea in 1960.

Sand composed of black basalt with grains of green olivine signifies a volcanic coastline. Here as the waves endlessly pound the rugged coastline, the rock breaks down. And in time, the relentless wave action rounds and polishes the grains. Olivine can vary in color from green to yellow-green depending on the quantity of iron in the crystal structure. Peridot is the name for gem-quality olivine and is the birthstone for August.

macro view of white round beach sand oocite

Joulter Cays, off Andros Island, Bahamas. Joulters Cays is located on the NE margin of the Great Bahamas Bank, about 10 miles north of Andros Island in the Bahamas.

Joulters Cay is unique, as the cay is made nearly entirely of ooids or oolites. These coated grains form around a nucleus. On Joulters, the nucleus is a tiny grain of shrimp feces; elsewhere, the nucleus might be a grain of sand or a shell fragment. As the grains are constantly agitated by the tides and the currents in the shallow carbonate-rich waters, concentric layers of calcium carbonate (in the form of aragonite) accrete and the grains “grow.”

Oolites range between .5 and 1 mm in diameter. Larger than 2 mm, they are called pisolites. Their size is controlled by rates of precipitation and abrasion. Oolites are also being formed in Great Salt Lake, Utah, at Shark’s Bay, Australia, and in the Persian Gulf in the vicinity of Qatar. Oolites and oolitic rock are also found in the fossil record.

“Sand collecting is popular worldwide,” says Leo. “For some it is a souvenir of travel. Others try to collect sand from all U.S. states or countries of the world. Still, others are interested in the geologic and biologic content of sand. The reasons for collecting are as varied as the people who collect.” Learn more about sand collecting from the International Sand Collectors Society at www.sandcollectors.org.

“I’ve met many good people through my interests in sand,” Kate says. “And I love to travel vicariously as I examine the sands and learn about the regional geology or marine environment from where they were collected.”

One result of Kate and Leo’s mutual interest in sand collecting is Splendid Sands, a website showcasing sands from around the world. Visit splendidsands.com and get ready to explore the science and beauty of sand.

This article appeared in the Beachcombing Magazine July/August 2020 issue.

Learn more about sand

View macro and micro views of Dania Beach, Florida in this short video

Leave a comment

All comments are moderated before being published