April 2002 AGGMAN Geology

Author’s Note: For the past few years this column has taken on issues of concern to the aggregate industry and has described how geology relates to those issues. While most folks who read this column probably have some knowledge of geology, it is a science with a history worth sharing. These next few articles will provide brief descriptions of some of the theories that have evolved into the science of geology.

These cottages in Castle Combe, which are typical of cottages in the English Cotswolds, are made from the local limestone, called oolitic because of its tiny egg-like grains, and honey-colored
because of the presence of iron.

Ancient scientists had some curious ideas about how rocks form. Greek philosopher Aristotle (384-322 B.C.) theorized that the heat or rays of the sun or other heavenly bodies penetrated into the Earth’s crust. When conditions were right, the rays would cause exhalations that ultimately gave rise to various kinds of stones, including the ancient white Pentelic marble used in the Parthenon in Athens. Roman naturalist Gaius Plinius Secundus (Pliny the Elder—A.D. 23-79) reported that stone, such as the travertine used in the Roman Colosseum being built at the time, could replenish itself in the quarries from which it was extracted. In 1672, English physician Thomas Sherley described in an essay, “The Probable Causes Whence Stones are Produced in the Greater World”, that stones were made of water that was condensed by the power of seeds with the assistance of “termentive odours.” Sherley was Physician in Ordinary to King Charles II, thus, it is no surprise that his hypothesis was based on observations of stones in the kidneys and bladders of men.
An alternate, and somewhat earlier, theory was based on Lapidifying Juice. The general principal was that a succus, or fluid body, was circulating through cracks, fissures and pores in the rocks where it was responsible for stalactites and stalagmites in caverns. Succus was also believed to be in the sea where it would deposit coral and pearls, and in the atmosphere, where its vapor would condense into stones that fell from the air.
German physician Georgius Agricola (1494-1555), commonly called the “Father of Mineralogy,” was a practicing doctor; however, it seems he never was terribly enthusiastic about his profession. Instead, he devoted most of his time to studies of mining and mineralogy. Agricola wrote that there is a class of rocks that are produced from collections of fragments (which are referred to as clasts) abraded from rock masses through the forces of running water. Succus flowing around these clasts transforms them into solid rock by supplying cement that fills up the spaces (interstices) between the clasts. Agricola, in essence, had correctly determined the origin of rocks that today are known as clastic sedimentary rocks, which indeed are formed by the cementation of rock fragments.
Agricola also thought succus could precipitate directly as a rock, and some limestones are created by direct precipitation. Calcium carbonate can be precipitated from shallow marine waters by warming, evaporation and concentration of the seawater. One rock formed this way is made out of carbonate grains that look like fish eggs, and for this reason is called oolitic limestone (for the Greek term oon, an egg). One of my favorites is the honey-hued oolitic limestone used throughout the English Cotswolds to build everything from great houses such as Blenheim Palace to simple farm walls. J.B. Priestley (1934) described the rock in his writings, “Even when the sun is obscured… these walls are still faintly warm and luminous… as if they knew the trick of keeping the lost sunlight of the centuries glimmering about them…”
Many other limestones form in the open sea from vast cemeteries of the remains of corals, shellfish and other sea life; these deposits may continue to grow over long periods of geologic time thanks to the teeming life of the sea. Each environment of deposition—reefs, shell beds or deep-sea oozes formed by countless microscopic shells of plankton—result in many types of limestones with many different properties and uses. For example, some reef rocks make excellent reservoirs for oil and gas, such as the Silurian reef rocks of the Michigan Basin, in the United States. Other reef rocks may be used as building stones. Black marble from the Fisk Quarry on the Isle La Motte in Lake Champlain, Vt., was used in the National Gallery of Art in Washington, D.C. The quarry has been preserved as a public park and the fossilized remains of what is often called “The World’s Oldest Coral Reef” can be seen in the exposed quarry walls and in rocks all around the property.
Some limestones form in the sea away from the sand and mud that borders the land. These rocks tend to be very chemically pure and can be used for the most demanding uses, such as in pharmaceutical, chemical and industrial applications. But if the sea is contaminated with muddy sediment, the resulting rock (commonly called argillaceous limestone) is a combination of carbonate material and clay. These rocks are put to more common usage such as crushed stone aggregate.
Limestones form in many other ways, resulting in rocks with a variety of properties that ultimately control their final use. The study of how these rocks form attracts geologists to beaches, coral reefs and warm tropical seas around the world. I must try to find a way to spend a field season at one of those localities to test Aristotle’s theory on the impact of the sun’s rays!

William H. Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey.

April 2002 Carved in Stone The Probable Causes Whence Stones are Produced				The Probable Causes Whence Stones are Produced By Bill Langer Author’s Note: For the past few years this column has taken on issues of concern to the aggregate industry and has described how geology relates to those issues. While most folks who read this column probably have some knowledge of geology, it is a science with a history worth sharing. These next few articles will provide brief descriptions of some of the theories that have evolved into the science of geology. These cottages in Castle Combe, which are typical of cottages in the English Cotswolds, are made from the local limestone, called oolitic because of its tiny egg-like grains, and honey-colored because of the presence of iron. Ancient scientists had some curious ideas about how rocks form. Greek philosopher Aristotle (384-322 B.C.) theorized that the heat or rays of the sun or other heavenly bodies penetrated into the Earth’s crust. When conditions were right, the rays would cause exhalations that ultimately gave rise to various kinds of stones, including the ancient white Pentelic marble used in the Parthenon in Athens. Roman naturalist Gaius Plinius Secundus (Pliny the Elder—A.D. 23-79) reported that stone, such as the travertine used in the Roman Colosseum being built at the time, could replenish itself in the quarries from which it was extracted. In 1672, English physician Thomas Sherley described in an essay, “The Probable Causes Whence Stones are Produced in the Greater World”, that stones were made of water that was condensed by the power of seeds with the assistance of “termentive odours.” Sherley was Physician in Ordinary to King Charles II, thus, it is no surprise that his hypothesis was based on observations of stones in the kidneys and bladders of men. An alternate, and somewhat earlier, theory was based on Lapidifying Juice. The general principal was that a succus, or fluid body, was circulating through cracks, fissures and pores in the rocks where it was responsible for stalactites and stalagmites in caverns. Succus was also believed to be in the sea where it would deposit coral and pearls, and in the atmosphere, where its vapor would condense into stones that fell from the air. German physician Georgius Agricola (1494-1555), commonly called the “Father of Mineralogy,” was a practicing doctor; however, it seems he never was terribly enthusiastic about his profession. Instead, he devoted most of his time to studies of mining and mineralogy. Agricola wrote that there is a class of rocks that are produced from collections of fragments (which are referred to as clasts) abraded from rock masses through the forces of running water. Succus flowing around these clasts transforms them into solid rock by supplying cement that fills up the spaces (interstices) between the clasts. Agricola, in essence, had correctly determined the origin of rocks that today are known as clastic sedimentary rocks, which indeed are formed by the cementation of rock fragments. Agricola also thought succus could precipitate directly as a rock, and some limestones are created by direct precipitation. Calcium carbonate can be precipitated from shallow marine waters by warming, evaporation and concentration of the seawater. One rock formed this way is made out of carbonate grains that look like fish eggs, and for this reason is called oolitic limestone (for the Greek term oon, an egg). One of my favorites is the honey-hued oolitic limestone used throughout the English Cotswolds to build everything from great houses such as Blenheim Palace to simple farm walls. J.B. Priestley (1934) described the rock in his writings, “Even when the sun is obscured… these walls are still faintly warm and luminous… as if they knew the trick of keeping the lost sunlight of the centuries glimmering about them…” Many other limestones form in the open sea from vast cemeteries of the remains of corals, shellfish and other sea life; these deposits may continue to grow over long periods of geologic time thanks to the teeming life of the sea. Each environment of deposition—reefs, shell beds or deep-sea oozes formed by countless microscopic shells of plankton—result in many types of limestones with many different properties and uses. For example, some reef rocks make excellent reservoirs for oil and gas, such as the Silurian reef rocks of the Michigan Basin, in the United States. Other reef rocks may be used as building stones. Black marble from the Fisk Quarry on the Isle La Motte in Lake Champlain, Vt., was used in the National Gallery of Art in Washington, D.C. The quarry has been preserved as a public park and the fossilized remains of what is often called “The World’s Oldest Coral Reef” can be seen in the exposed quarry walls and in rocks all around the property. Some limestones form in the sea away from the sand and mud that borders the land. These rocks tend to be very chemically pure and can be used for the most demanding uses, such as in pharmaceutical, chemical and industrial applications. But if the sea is contaminated with muddy sediment, the resulting rock (commonly called argillaceous limestone) is a combination of carbonate material and clay. These rocks are put to more common usage such as crushed stone aggregate. Limestones form in many other ways, resulting in rocks with a variety of properties that ultimately control their final use. The study of how these rocks form attracts geologists to beaches, coral reefs and warm tropical seas around the world. I must try to find a way to spend a field season at one of those localities to test Aristotle’s theory on the impact of the sun’s rays! William H. Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey.