November 2006

The Stuff of Dreams

From longer golf drives to pain relievers, the black sand known as ilmenite colors many aspects of everyday life.  

Imagine you are walking along an ocean beach. In the distance, you see an aggregate operation. You look down and notice bands of black sand that have collected near the surf’s edge. You hear a jet fly overhead. You look up, but your gaze is interrupted by a deranged golfer with a replacement hip implant, nose covered with sunscreen, madly waving his titanium club to chase a dog off the course. You ask yourself, “What do these images (shown in italics) have in common?” You put the turmoil aside and drift off to dreamland — to a world you can see in a grain of sand.

Most of the black sand on the beach is made up of mineral grains called ilmenite. The aggregate operation is one of the occasional operations that produce ilmenite as a byproduct of sand and gravel mining. 

Ilmenite is a source of titanium — a white metal, stronger, yet many times lighter than steel. It naturally occurs in meteorites, the sun, and the moon, as well as in plants and human bodies. Titanium alloys are used in high tech airplanes, jet engines, missiles, and space vehicles. Medical grade titanium implants are hypoallergenic, and bone growth can adhere to them. It’s no surprise, then, that patients around the world receive more than 1,000 tons of titanium implants each year. 

For you duffers, titanium golf clubs can be manufactured where the “sweet spot” of the club head is the size of a quarter — much larger than the tee-size sweet spot on traditional clubs. This larger sweet spot may result in increased distance and accuracy.

However, the overwhelming use of ilmenite is in the manufacturing of titanium dioxide (TiO2) pigment. The pigment has a pure white color, great luster, good endurance, and it effectively hides whatever it covers. The pigment is used primarily in paints, but it also provides color for rubber, plastics, textiles, ink, cosmetics, leather, ceramics, and paper. TiO2 or other titanium compounds are used for coating electric welding rods; in toothpaste, desalination plants, electrical components, glass products, and jewelry; and as an ultraviolet blocker in sunscreen.

And for dog lovers, Lucy and Rosie (pictured with me in the photo above) want you to know TiO2 is used as a colorant in dog food.

Ilmenite occurs in igneous rocks where it crystallizes out of the molten magma before most of the other minerals. Because ilmenite crystals are heavier than magma, they collect in layers at the bottom of the magma chamber. These layers create a rich ore body for titanium miners.

Ilmenite is a source of titanium, a white metal that is stronger,
but lighter than steel.

Large amounts of ilmenite come from black sand. When ilmenite-bearing rocks are weathered, rivers and streams transport grains of ilmenite and other minerals to the sea. Those minerals are carried back onto land by waves that wash up and down the beach. The waves carry the lighter minerals such as quartz grains back into the sea, leaving behind the heavier grains, including ilmenite. Throughout millions of years, large amounts of heavy mineral sands collect in beach deposits.

Worldwide, nearly 6 million tons of ilmenite are produced every year. Black sand deposits are mined on every continent except Antarctica. The largest deposits in the United States are found along the coasts of Florida, Georgia, the Carolinas, New Jersey, and Virginia. However, the largest heavy mineral sand industry is located on the East and West coasts of Australia.

A barking dog snaps you out of your stupor. You drift away from the world of ilmenite back to this world. You see no beach, no golfer, and no aggregate operation. Instead you see Lucy and Rosie staring at you from this page of Aggregates Manager, which, by the way, contains titanium dioxide.

And if you are wondering where I came up with the title for this article — some pain relievers that also help you to sleep contain TiO2 as a colorant. Sweet dreams!

October 2006

The Sands of Time

Whether measured through an hourglass or a beachfront, sand and stone show the effects of time

The banner on the front of this issue proclaims that Aggregates Manager is “Celebrating 10 years serving aggregates professionals.” I have shared a fair part of that history. My first column appeared in the January 1998 issue — this is my 100th article. 

The theme of this year’s column is, “To see a world in a grain of sand.” I make the point that the processes relating to the weathering, transport, and deposition of sand commonly take place throughout immense periods of time — referred to as geologic time. However, some moments in geologic time are more exciting than others. I will use this anniversary to tell you some of the things that happened in the world of sand during the 8 years and 10 months that I have been writing “Carved in Stone.”

Sand commonly begins as solid rock, which, throughout geologic time, breaks down into smaller and smaller pieces. Weathered rock slowly moves down-slope where it accumulates at the base of hills and mountains. Since the first “Carved in Stone” article, more than 5 billion tons of weathered rock have moved in this manner.

But downslope movement is not always measured in geologic time. “The Old Man of the Mountain,” featured on the New Hampshire quarter (minted in 2000), was one of the state’s most prized natural attractions. The Old Man had been gazing across the countryside for thousands of years. On May 3, 2003, he crumbled to the ground in a sudden rock fall. During geologic time, his remains will become grains of sand.

The phrase “moving at a glacial pace” is a good description of geologic time. Glaciers inexorably grind solid rock into tiny pieces. Since my first AggMan article, glaciers around the world have generated about 40 billion tons of sand, gravel, boulders, and clay.

However, what constitutes a glacial pace might surprise you. The Mendenhall glacier, near Juneau, Alaska, advances about 2 feet per day. At that rate, the glacier would have advanced 1.2 miles during the period from my first AggMan article to the 100th one. Consider also that ice is melting from the front of the Mendenhall Glacier faster than the ice is advancing. Overall, the front of the glacier is retreating at a rate of about 32 feet per year. Like the Old Man of the Mountain, ice retreat takes place in spurts. During one single year, 2004, the east side of the glacier retreated 656 feet.

Rivers and streams carry grains of sand from glaciers and weathered slopes to the sea. During the “Carved in Stone” geologic mini-epoch (8.83 years) more than 210 billion tons of sediment have been carried to the sea. Some sand grains are carried back onto land by waves that wash up and down the beach. Ocean waves also nibble away at beaches and cliffs — waves eroded more than 2 billion tons of material during the same period of time. By now you probably have figured out that beach erosion takes place in fits and starts. In the Pacifica, Calif., area, the long-term erosion rate for cliffs is roughly 8 inches per year. However, as El Niño raged in 1997-98, the cliff faces in this area were eroded more than 30 feet during a single month — accounting for almost 50 years of average erosion.

Incidentally, since I penned my first “Carved in Stone” article, aggregate producers around the world have moved about 130 billion tons of crushed stone, sand, and gravel. A lot can happen in one tick of the geologic clock, especially when seen in the world of a grain of sand. AM

Author’s note: The best events of the last 8 years and 10 months were the arrivals of Rob (son-in-law), Donovan and Delaney (grandkids), and Lucy and Rosie (Cavalier King Charles Spaniels) — truly memorable occasions.

September 2006

The Sands of War

Geologic studies of sand deflate World War II balloon bombs.

During the second world war, the Japanese attached incendiary and anti-personnel bombs to balloons and released them into easterly wintertime jet stream winds to float 5,000 miles across the Pacific. They named the weapons “fusen bakudan,” which means balloon bomb.

On Nov. 5, 1944, one of these balloon bombs landed near San Pedro, Calif. During the next few months, about 300 confirmed landings or sightings were made as far north as the Aleutian Islands, as far south as Nogales, Ariz., and almost as far east as Detroit.

The balloons were crafted from layers of washi (paper made from mulberry bushes) glued together with flour made from konnyako (a Japanese tuber called devil’s tongue). The balloons were 33 feet in diameter and, when filled with hydrogen, could lift approximately 1,000 pounds. They carried an altimeter that released hydrogen when the balloons rose above 38,000 feet during the heat of the day. The balloons also carried three dozen ballast bags filled with between 3 and 7 pounds sand. Small explosive devises released pairs of ballast bags when the balloons dropped below 30,000 feet during the cold of the night. When the ballast bags were all expended, the balloon was destroyed and its payload of bombs would descend upon whatever lay below.

Most of the ballast bags were released in the trip across the Pacific, but a few balloons crashed without exploding. Under extreme secrecy, some small amounts of sand recovered from ballast bags at crash sites were given to the Military Geology Unit (MGU) of the U.S. Geological Survey.

Military intelligence thought the balloons were launched by submarine landing parties from beaches on the Pacific coast of North American or small Pacific islands. However, the MGU determined that the sand had come from a beach in Japan. Paleontological studies by the MGU identified more than a hundred types of fossil and recent diatoms contained within the sand samples, which was evidence that the sand came from a salt water beach. Scientists also found foraminifera (see Aggregates Manager April 2006) species that had been described only in geologic papers about beaches north of Tokyo. Furthermore, the sand did not contain any coral, thus eliminating all beaches south of Tokyo Bay. 

Mineralogical studies revealed an unusual set of trace minerals including minerals known to be of volcanic origin and minerals associated with metamorphic rocks. Consequently, the MGU looked for areas north of Tokyo Bay with both volcanic and metamorphic rocks upstream from the beach. Further detailed studies of trace minerals led the MGU to the determination that the sand samples probably came from either a site along the great beach at Shiogama, close to Sentai, Japan, or from the Ninety-nine League Beach at Ichinomiya, Japan.

Photo interpreters made detailed studies of these areas and identified two hydrogen-producing plants near Ichinomiya. American B-29 bombers destroyed these plants in April 1945, putting an end to the balloon bomb project.

Epilogue: On March 5, 1945, five Sunday-school children and a minister’s wife on a picnic discovered and attempted to move a balloon bomb that had crashed near Bly, Ore. They were killed when the bomb exploded. These six people were the only casualties of World War II from hostile action on the U.S. mainland.

August 2006

Love Legend in the Sand

A study of oolitic sand in the Sedir Island suggests that the legend of Cleopatra’s Beach may be real.

Cleopatra’s Beach is located on Sedir Island in Gökova Bay in the Aegean Sea. The beach is tiny — only about the size of a football field end zone. Nevertheless, it is one of the most famous beaches in Turkey. Its celebrity status is due in part to the legend that a love-struck Mark Antony had shiploads of sand brought from Egypt to create a beautiful sandy beach for his new bride Cleopatra.

The sands on Cleopatra’s Beach are different from mineral sands, which are formed by weathering of pre-existing rocks (Aggregates Manager, March 2006), and biogenic sands, such as the Star Sands of Taketomi-jima, which are composed of the remains of living organisms (Aggregates Manager, April 2006). The sands on Cleopatra’s Beach are oolitic sands, and represent the third category of sand — precipitated sand.

Oolitic sands are composed of ooids (from the Greek word oon meaning egg), which are spherical grains that resemble fish eggs and are generally smaller than the head of a pin. They commonly consist of calcium carbonate and usually form in high-energy, super-saline shallow marine environments.

Unlike mineral or biogenic sand grains that are created through the breaking down of pre-existing rock, shells, coral, and so forth, ooids form by building up material. They do this by two different methods: (1) the physical attachment of fine-grained material as they roll around on the shallow sea floor, much the way a snowball accumulates more snow when you roll it around to make a snowman; and (2) by the chemical precipitation of material out of solution, much like rock candy grows on a string in supersaturated sugar water. In both cases the ooids form around some “seed” or nucleus.

Cleopatra’s Beach is the only known oolitic sand beach along the Turkish coast. The ooids have all the typical features of high-energy, shallow-marine ooids, but Gökova Bay is a small, well-protected, very-low-energy bay. In addition, instead of being shiny and white, the ooids have a pale brown-creamy color and a dull surface luster, characteristics perhaps acquired by aging in a low-energy environment that is insufficient for ooid formation and maintenance. These observations suggest that the ooids are not in their natural environment.

Geologists El-Sammak and Tucker (as well as other researchers) have compared oolitic sand from Cleopatra’s Beach with sand from the northern coast of Egypt, west of Alexandria, the only place in the Mediterranean with abundant oolitic sands. In terms of size, shape, internal structure, and mineralogy, the Cleopatra ooids show great similarities to those from west of Alexandria. On the basis of physical properties, the hydrographic conditions at Gökova Bay, the relatively small quantity of oolitic sand on the tiny beach, and the absence of oolid sand anywhere else in Turkey, they concluded that the oolitic sand was brought to Cleopatra’s beach from somewhere else; most likely the northern Egyptian coast.

The geologic studies lend credence to the legend of Cleopatra’s Beach. Calculations suggest that about 15 Roman barges could have transported the sands from Egypt to Sedir Island in Gökova Bay. If the sand was brought to the island during Cleopatra’s lifetime, as the legend professes, the beach has persisted in the storm-protected, low-energy conditions for more than 2,000 years, thus making it one of the oldest love legends in the sand. 

July 2006

CSI: California

An early forensic scientist uses sand to solve the mysterious disappearance
and murder of a California priest.

During the last few months, this column has described a variety of worlds that can be seen in different grains of sand. But are sand grains really that different from one another, or is this column just presenting examples of rare occurrences? The photographs accompanying this article, all from beaches in California, demonstrate that sands are indeed different from one another. To support this contention, I offer as evidence the following account: The Sands of Crime.

On the evening of Aug. 2, 1921, a man wearing goggles and shielding his face with the collar of a heavy overcoat came to the rectory of Holy Angels Church in Colma, Calif. The man said that 58-year-old Father Patrick F. Heslin was needed for a sick call in Salada Beach. Father Heslin, dressed in official clerical garb, left the rectory in a touring car driven by the clandestine caller.

A ransom note was received stating that Father Heslin had been kidnapped. No further contact was made, and it was assumed that the priest had been murdered.

William A. Hightower, an unemployed master baker, told the archbishop he had clues to the whereabouts of the kidnapped Colma priest, but the church officials ignored him. On Aug. 10, Hightower led newspaper reporters and policemen to Salada Beach (now Sharp Park in Pacifica), where Heslin’s corpse was buried.

Enter University of California, Berkley, chemistry professor Edward O. Heinrich. Heinrich had graduated from University of California at Berkeley with a degree in chemistry in 1908 and had held a number of positions in various cities where he learned to combine his interest in chemistry with criminal investigation and detection.

Heinrich examined the handwriting on the ransom note and informed the police that the writer “had the hand” of a baker and decorator of cakes. When Hightower told the police that he had heard where the body of Father Heslin was buried, his status as master baker immediately put him under suspicion. Perhaps he knew more than he admitted.

Heinrich visited the place on the California beach where the body of Father Heslin and a number of other objects of physical evidence, such as boards from a tent floor, were found. He studied grains of sand recovered from Hightower’s knife and pronounced them similar to the sand on the beach where the body was found. A tent containing an abundance of sand was found in Hightower’s room, and Heinrich confirmed that the sand in the tent matched that from Hightower’s knife.

Apparently Hightower had kidnapped and murdered Father Heslin. He kept Heslin’s body in a tent on the beach for several days and then buried it in the sand. Afterward, he reported to the police that he had received information about the location of the body.

The trial of William A. Hightower resulted in conviction. He was sentenced to life imprisonment, and spent more than 40 years at San Quentin Penitentiary. Hightower was released from prison on May 20, 1962, at age 86.

Edward O. Heinrich (1881–1953), also known as “The Wizard of Berkeley,” was one of the pioneers of professional forensic sciences. The kidnapping and murder of Father Patrick Heslin, arguably Heinrich’s most famous case, provided the link of a suspect and his knife to the scene of a crime, all via common, but distinctive, beach sand.

-Bill Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey and can be reached at 303-236-1249.

June 2006

Golden Sands
To see a world in a grain of sand:
Panning for gold may not be so foolish.

Although pyrite is commonly mistaken for gold, some sand and gravel producers net major profits by collecting gold as a byproduct.

Imagine yourself beside a stream, holding a pan with sloping sides and a flat bottom. You alternately fill the pan with stream sediment, dip the pan in and out of the stream, shake it about, gently swirl it, and tip it to and fro washing out some of the sediment. After many hours of work, repeating this exercise over and over, you suddenly see sparkling yellow metal, just like the shiny grains in the accompanying photo.

Gold!

Well, dag nab it, not quite. Those metallic sand grains shown here are actually pyrite-iron sulfide — Fool’s Gold. The sand was collected from Contrary Creek, Va., an area of historic gold and pyrite mines and prospects. So it might have been gold — but sadly, it isn’t!

The process of washing material in a pan as described above is referred to as “panning.” Some early prospectors carved gold pans from large blocks of wood and smoothed them with sand from a streambed. But the most popular gold pan was the steel pan. Today, many people search for gold using a pan molded from tough plastic. Plastic pans are about one quarter the weight of a steel pan, are rust proof, can be textured with a fine “tooth” and riffles that can trap the gold, and can be made black so that even the tiniest flakes of gold can easily be seen.

Panning is the most common, and least expensive, method for a prospector to separate gold from the silt, sand, and gravel of the stream deposits. Panning is a tedious, back-breaking process which, although appearing to be a simple task, requires years of experience to master. Nevertheless, there are few thrills comparable to finding gold collected in the bottom of your pan. Some aggregate producers might give it a try — for reasons you will soon see.

Although gold is relatively scarce in the earth, it is concentrated by natural geologic processes to form commercial deposits of two principal types: lode deposits and placer deposits. Lode deposits are the targets for the “hard rock” miner. Placer deposits, the target of panners, are concentrations of gold weathered from lode deposits that have accumulated in terraces, floodplains, and channels of streams.

Gold production from placers historically took place in the western United States, although limited amounts of gold have been washed from some streams draining the eastern slope of the southern Appalachian region and from some New England states.

Placer gold can still be found in the sediments of active streams, and really valuable concentrations can be found in areas where river gravels and sediments are commercially mined — gravel pits. Some sand and gravel producers are aware of this and recover placer gold as a byproduct of sand and gravel extraction. This has been going on in some western states since at least the 1960s.

A number of techniques are used to capture gold from aggregate mining operations, but one of the simplest techniques is to screen the material coming from the pit, split off some of the sand, and run it over a sluice box lined with a carpet mat that catches the gold.

Is it worth it? About a million dollars of placer gold is mined in Alberta, Canada, every year — all a byproduct from gravel extraction. So, if you produce sand and gravel from streams that drain watersheds containing historic gold mines, you might want to get yourself a “gold dish” and see if something pans out.

May 2006

The Tragedy of Martinique
To see a world in a grain of sand:
West Indies sand speaks of a violent past.

Figure 1: Volcanic sand from St. Pierre Beach, Martinique.  Photo courtesy Loes Modderman,  Nijimegen, Netherlands

Notice anything special about the sand grains in Figure 1? Some of the grains look like regular sand, but those rod-shaped grains sure look different! The sand was collected from a tranquil beach on the island of Martinique in the West Indies. It is comprised of basalt, rhyolite, olivine, and augite (the elongated crystals. These sand grains are of volcanic origin, and unlike their idyllic Caribbean setting, they speak of a violent past.

The story begins in early 1902 and takes place near St. Pierre, a port city in Martinique situated near the base of a volcano named Mount Pelée. The volcano had just awoken from a half-century nap. Tremors shook the earth and Pelée spewed volcanic ash and sulphuric gases over neighboring towns. These nightmarish conditions worsened when the ashfalls and tremors drove ground-dwelling insects and snakes from the slopes of Mt. Pelée into St. Pierre and outlying villages. Horses, pigs, and dogs screamed as red ants bit them while thousands of poisonous snakes joined the fray. An estimated 50 people, mostly children, along with some 200 animals, died from snakebites.

On May 5, the crater rim gave way, sending a torrent of scalding water mixed with loose volcanic debris cascading down the River Blanche. This large volcanic mudflow is referred to as a lahar. It had the consistency of wet concrete, and carried debris ranging from ash to 30-foot boulders downslope at speeds of more than 60 miles per hour. The lahar buried everything in its path including people, animals, and buildings. It continued into the sea, generating a nearly 10-foot-high tsunami that flooded the waterfront of St. Pierre.

Despite this activity, the government declared that St. Pierre did not need to be evacuated. To the contrary, thousands of people from neighboring towns being bombarded by the ash sought refuge at St. Pierre, increasing the population to about 28,000.

At about 7:50 a.m. on May 8, witnesses located out of harm’s way reported a thunderous explosion followed by a large black cloud that rushed down Mt. Pelée. The cloud was a fluidized mixture of ash, rock fragments, and toxic gases. It flowed down Pelée much like a snow avalanche, except that it was fiercely hot and moved at hurricane-force speeds in excess of 60 miles per hour. At the time, the phenomenon was given the name “nuée ardente” (glowing cloud), but today is referred to as a pyroclastic flow. It is now considered the signature characteristic of a Peléean-type eruption.

In less than 1 minute, the pyroclastic flow struck St. Pierre with devastating force. The blast was powerful enough to turn 1-yard-thick masonry walls into rubble. A 3-ton statue was blown from its mount and carried more than 50 feet. The temperature within the flow probably was more than 900° F, hot enough to burn and carbonize wood. The searing heat ignited huge bonfires. Thousands of barrels of rum exploded, sending rivers of the flaming liquid through the streets and into the sea. The master cathedral bell was melted into a crumpled mass. The flow destroyed at least 20 ships anchored offshore, which were either capsized by the force of the wind or set ablaze by the heat of the gases. Of the 28,000 people in St. Pierre, there were only two known survivors.

So how does the sand tell this story? The crystal faces on both ends of the augite crystals indicate that they formed in molten magma within the crater that was at a temperature such that the magma could begin to solidify. The crystallizing magma plugged the volcano, and pressure built up beneath the plug until Pelée explosively erupted, generating the devastating pyroclastic flows. While these crystals may not have come from the 1902 eruption that was responsible for the carnage described above, they do represent an explosive eruption at Mount Pelée.

April 2006

Seeing Stars
To see a world in a grain of sand:
Taketomi Island’s star sand takes the spotlight.

The beaches on the southern end of Taketomi Island (Taketomi-jima) in Japan contain absolutely dazzling grains of sand called star sand. An old Okinawan folktale describes how star sand came into being. The tale tells how the Almighty God told Southern Cross, the mother of star babies, to have her children on the south side of Taketomi-jima, “where the current is warm and slow.” Southern Cross went to the ocean by the island and gave birth to many babies.

The Seven-Dragon God was angered by this and told a giant serpent to eat the babies. After killing the babies, the serpent spit them out and their bodies turned into tiny star-shaped particles of sand. There was a worship place at the seashore where the star babies’ bodies were.

A kind goddess found the dead star babies, gathered them up, and put them in her incense burner. When the villagers came to worship the goddess, the villagers burned the incense and the star babies floated with the smoke back to their mother in the sky. That is why when you look in the sky at the Southern Cross, there are so many baby stars circling around their mother.

A more scientific explanation focuses on tiny, amoeba-like, single-celled organisms called foraminifera (forams, for short). Forams live in immense numbers in the sea, feeding on even smaller diatoms and other nutrients. Forams are usually less than 1 mm in size, but some can be as large as a few centimeters — not bad for a single-celled organism.

Even though forams are among the simplest organisms in the animal kingdom, some of them are capable of creating beautiful, complicated shell houses (referred to as tests) in which to live. When forams die, their tests fall to the bottom of the sea in what has been described, because of the immense numbers of some species of forams, as neverending rain.

The shallow tropical marine environment near Taketomi-jima is characterized by high salinity and pH, which enriches the amount of carbonate ions (CO3-2) in the seawater. This is, in part, responsible for the high production rates of a special group of star-shaped foraminifera called Hoshi-suna. The Hoshi-suna uses the carbonate ions to produce calcium-carbonate (CaCO3) tests as large as 3 mm. The Hoshi-suna clings with their spines to the coral substrate to resist the high water energy at the reef front. When they die, the empty tests are transported by waves to the beach.

Despite their tiny size, a great deal of information can be gained by studying foraminifera. About 250,000 species of living and fossil forams are recognized. Some species have well-defined preferences for certain environmental conditions, and their presence in sediment is an indicator of environmental conditions over geologic time.

Paleontologists can examine the forams in rock samples and determine the geologic age and environment when the rock formed. By doing so, geologists can reconstruct what the earth looked like during past geologic times. Some forams are associated with oil-bearing rocks, which is why the oil industry is a major employer of paleontologists who specialize in these fossils.

Some sedimentary rocks are composed primarily of foraminiferan tests. For instance, the pyramids of Egypt are made of nummilitic limestone, which consists almost entirely of foram tests. Nummelites are a type of lenticular foram that reach about 6 cm (2.4 in) in diameter — but that’s another story!

March 2006

Nature's Aggregate Operation
Man-made processes mimic those already existing in the natural environment.

Sand starts as solid rock. Throughout  time, nature breaks big rocks into smaller and smaller pieces until they eventually become grains of sand. Aggregate operators should be quite familiar with this process because they, too, produce sand by crushing large blocks of rock into smaller and smaller pieces. Draw upon the science in your soul, and imagine an aggregate operation where the equipment has been replaced with natural geologic processes.

Figure 1: Sand from Grosses Wasser, Wallis, Switzerland

Figure 2: Sand from South Point, Hawaii.

Drilling, blasting, crushing — When bedrock is exposed at the surface of the Earth, cracks start to form (drilling). Water flows into these cracks, and when it freezes (or roots grow into the cracks), the rocks are pried apart (blasting and crushing). Gases from the atmosphere and chemicals such as organic acids in the soil mix with the water and chemically alter and weaken the rock. Some rock minerals are dissolved or weathered into silt or clay particles. The more-resistant minerals remain as rock fragments and together with silt and clay, create nature’s surge pile — loose, unconsolidated residual soil waiting to be processed.

Conveyors, secondary crushing, screening, classifying — Gravity, often aided by water, moves the residual soil downslope where it accumulates in stream valleys. Streams (conveyors) move the rock fragments and subject them to abrasion and rounding (secondary crushing). The water sorts the particles by size and density (screening and classifying), and eventually some of the stream-transported material is deposited on sand bars (stockpiles). Just like manufactured sand, the mineralogical composition of natural sand depends on the rock from which it came.

Quartz, a hard, durable mineral, usually survives nature’s rock-disintegration process. Quartz is so common that the word “sand” oftentimes is considered to be quartz sand. However, sand comes from a variety of rock types, with each type of rock yielding a specific type of sand. So if you identify the different minerals in a specific rock, you might be able to predict what type of sand will be generated (either naturally or artificially) from that rock.

This job might seem to be insurmountable because there are thousands of minerals. But don’t despair. Most rocks contain only a few of the 20 most common minerals including quartz, feldspar, mica, pyroxene, hornblende, olivine, garnet, calcite, and dolomite.

For example, the sand shown in Figure 1 probably came from a granitic rock. It contains mostly quartz (clear or milky grains) and feldspars (pink and white opaque grains) with lesser amounts of dark minerals such as mica, hornblende, or pyroxene. Quartz and feldspars are both very strong, generally non-reactive minerals. Crushing granitic rock is likely to make sand rich in quartz and feldspars, which commonly works well in portland cement concrete. The sand grains are also likely to have angular shapes, which are beneficial for use in asphaltic concrete.

In contrast, the sand in Figure 2 came from a volcanic rock. The sand consists mostly of the mineral olivine (yellow-green, translucent grains) with some obsidian (black, opaque grains). Obsidian is subject to the alkali-silica reaction, and sand manufactured from rock containing obsidian might require special treatment if used in Portland cement concrete.

There are countless types of rocks on the earth. Therefore, it should be no surprise that if you look carefully, you will see there are countless types of sand, the products of nature’s aggregate operations.

February 2006

Blown Away
Carried  by the wind, eolian sand becomes rounded and frosted through
 the process of saltation.

eolian (e-o’-li-an) Pertaining to, caused by, or carried by the wind. 
Origin: In Greek mythology, Aeolus was keeper of the winds.

Geologists refer to sand that has been moved and deposited by the wind as eolian sand. To get a better feeling for the subject, take yourself back to a time when you were at the beach or in the desert, bare footed, wandering around a sand dune. Remember that strange sound of the sand squeaking or groaning with every footstep? If it was windy, did you feel something like tiny bugs stinging your ankles? Both of these sensations relate to the wind-blown nature of sand.

If you had looked closely at the dune on a windy day, you would have seen that the surface of the dune appeared to be in motion and that the stinging was not from bugs, but was from sand grains that appeared to jump into the air to bite you. This is because most eolian sand grains move by a process called saltation where they bounce along as they are lifted into the air, fall back to the ground, and bounce up again.

The impact of the falling grains dislodges additional sand grains that are sent bouncing in the down wind direction. The grains will reach about ankle height (ouch), and during intense storms may occasionally reach heights exceeding 6 feet. You sometime can see the results of saltation on wooden fence posts or telephone poles in desert regions where the bottom few inches of the pole has been severely abraded by the eolian sand.

Some hard, durable sand grains, such as those made of quartz (shown in Figures 1 and 2), survive collisions with other grains. The eolian sand grains (Figure 1) have been rounded and frosted from abrasions during saltation. (The orange color is from a thin iron oxide coating on the sand grains.)

In contrast, the angular, clear sand grains (Figure 2) were moved by water. The water buffered the sand grains, preventing them from directly colliding with one another as frequently, thus preserving the angular shapes of the grains.

Saltation is just one way that granular materials such as sand move. Sand sometimes acts like a solid and sometimes acts like a fluid, and the transition from one behavior to the other can be very rapid. For example, sand in the back of a dump truck will sit as a solid pile, even as the truck bed begins to tilt. When a certain angle is reached, the sand pile will collapse and flow out of the truck like a river of sand.

You might also have experienced this phenomenon while walking on a sand dune. If you stepped in just the right place, you might have ended up riding down the face of the dune, ankle deep in a sand avalanche. And that squeaking sound you heard as your foot compressed the sand? Credit that to the texture and roundness of the eolian grains and the friction of those grains as they slide against one another.

Or perhaps it is Aeolus groaning while he is blowing around the sand.

January 2006

To See a World in a Grain of Sand
The physical and chemical properties of sand influence their use in the everyday world.

Quartz sand from Talin, Estonia.

Sand composed of shell fragments from O’Carrol’s Cove, County Kerry, Ireland.

“Star sand” from Taketomi-jima, Okinawa, Japan.

Multicolored sand from Lake McDonald, Glacier National Park, Montana.

As a youngster, I spent summers at the shore on the coast of New Jersey. I enjoyed many hours wandering the sandy beaches, sifting the sand through my fingers, and squeezing it between my toes. I still remember the brilliant white color of those beaches. Along the water’s edge, little ribbons of black sand grains stood out from the rest of the sand. Elsewhere, pink-colored shell fragments would collect where the waves washed the beach. The changing tides and winds constantly modified the area. Every day, I had something new to explore.

Even as a kid, I noticed that all sand was not alike. The white sand from the beach was different from the black sand ribbons and pink shelly sand from the surf’s edge. Later in life, as a geologist, I discovered just how different one grain of sand can be from another.

Sand is commonly produced by the physical and chemical weathering of rock. Sand can be made of many different minerals, but quartz — being strong, hard, and durable — is by far the most common.  By determining the mineral content of sand, one can make certain assumptions about the rocks from where it came.

Sand can also be made of shells, shell fragments, or other hard remains of animals or plants. By understanding what animal or plant the sand came from, one can make assumptions about the environment where the animals or plants used to live.

Sand grains come in all kinds of shapes. They can look like spheres, footballs, potatoes — some even look like little stars. The surface of sand grains can be smooth and rounded, sharp and angular, and flat and flakey. Some shapes give away secrets about the origin of the sand, while other shapes tell of arduous journeys that the sand grains have taken.

Sand can be colorless, white, black, pink, green, tan, red, yellow, orange…nearly every color of the rainbow. Some sands contain only one mineral and are monochromatic. Others are mixtures of different minerals (or shells, and so forth) and can be multicolored. Some sand grains are downright gorgeous!

All of this information — size, texture, mineralogy, fossil content, and color — define the physical and chemical properties of the sands that ultimately influence their use in the human world. These properties are important because without specific kinds of sand we would not have glass (quartz), cast iron equipment (foundry sand), paved roads (construction sand), chickens (grit), roof shingles (granules), and on and on.

Throughout the year, this column is going to take a close look at sand — one of the world’s most common materials. And if you have a little bit of science in your soul you, too, will be able…To see a world in a grain of sand. 

Author’s note: The title of this article is from Auguries of Innocence by William Blake (1757-1827). The poem is too dark, deep, and complicated for me, but then, sand is pretty complicated, too.