Geotimes Banner

Geotimes is now


Customer Service
Geotimes Search

GeoMarketplace Link

EARTH magazine cover

  Geotimes - July 2007 - Energy & Resources

A blight on ethanol
Finding diamonds in your backyard?

Mineral Resource of the Month: Talc

Ethanol is unlikely to improve air quality and may even increase health risks. Or so says a controversial report on the human health effects of converting gasoline-powered cars and trucks to run on this plant-based alternative.

Proponents of ethanol say that it will reduce global warming, air pollution and U.S. reliance on foreign oil, says Mark Jacobson, an atmospheric researcher at Stanford University in Palo Alto, Calif., and author of the study, published April 18 in Environmental Science & Technology. As air pollution is the seventh leading cause of death worldwide, it is important to find out whether ethanol actually is cleaner and better for people and the environment than gasoline before the United States plunges further into developing the fuel, Jacobson says.

Jacobson used a sophisticated atmospheric model to compare the emissions of various chemicals from automobiles running on E85, a blend of 85 percent ethanol and 15 percent gasoline, with those running on traditional gasoline in the year 2020, when ethanol-fueled automobiles are expected to be widely available in the United States. The model then estimated the complex environmental interactions that occur with emissions to determine the impact on public health. Such interactions vary based on the amounts and types of chemicals released, ambient temperatures, sunlight, clouds, wind and precipitation, among other factors. This is the first atmospheric model to incorporate this many factors and complex chemical reactions, says Mark Delucchi, a research scientist at the Institute of Transportation Studies at the University of California at Davis, who specializes in economic, environmental, engineering and planning analyses of current and future transportation systems.

Jacobson modeled the atmospheric reactions for the entire United States, as well as specifically in the Los Angeles, Calif., area, as it is home to 6 percent of the U.S. population and historically has had the most polluted air in the United States, therefore lending itself to being the test bed for most U.S. air pollution regulations.

Jacobson’s calculations showed that if the entire U.S. fleet were replaced by vehicles running on E85 in 2020, ozone-related deaths would increase by 4 percent across the United States and by 9 percent in Los Angeles. Furthermore, ozone-related hospitalizations would increase by nearly 1,000 people per year across the United States, and emergency room visits caused by asthma and other breathing complications would increase by more than 1,200 people per year. Cancers caused by emissions would stay about the same with either ethanol or gasoline, as ethanol emissions increase some carcinogenic chemicals but reduce others, he says.

The overall conclusion of this modeling research — that ethanol will not significantly improve air quality and may even worsen it — is “unassailable,” Delucchi says. “The epidemiological results follow” from the assumptions Jacobson included in the models, Delucchi says.

Although this study is creating quite a stir, Delucchi says, this is the first model sophisticated enough to reach a conclusion about future air quality and human health ramifications from the use of ethanol. Furthermore, he says, the study supports research Delucchi and colleagues at Davis have done on the emissions of biofuels throughout the fuels’ entire lifecycle, which suggests that biofuels are not nearly as clean as is publicly portrayed.

Other researchers have found similar results, says David Pimentel, an ecology and agricultural sciences professor at Cornell University in Ithaca, N.Y. Even the Environmental Protection Agency recognized that certain ozone precursors, such as volatile organic compounds and nitrogen oxides, could increase with ethanol usage, as published in the agency’s April 2007 Renewable Fuel Standard Program report. “It’s not a clean fuel,” Pimentel says, and promoting it as the answer to energy security and climate change challenges is “a major boondoggle,” brought about by “big money and politics.”

Others, however, tout evidence of improved air quality since ethanol has been blended into fuels in California, New York and Wisconsin, among other states. According to a March 2006 report by the Better Environmental Solutions and Renewable Energy Action Project, tests show a “consistent association between ethanol blending and reduced ozone pollution.” However, the authors of the report caution that they cannot say that the air is cleaner solely because of ethanol.

Jacobson offers the same caveat on his research. The question of causation is indeed “very hard to prove from data analysis alone,” he says. “But then again, after Brazil converted to ethanol in the 1970s, ozone levels spiked,” he says. Models can determine cause and effect to a degree, he says, and his models show increasing ethanol usage as a cause of the increased pollution.

The bottom line, Delucchi says, is that mounting evidence suggests that it would be “virtually impossible” to prove that ethanol will significantly improve our air quality and climate in the future. Instead, Jacobson says, “it’s important to look at gas and ethanol in comparison to other nonpolluting sources, such as electric and hydrogen vehicles powered by renewable energy.”

Megan Sever

Back to top

Stornoway Diamond Corporation
The odds of finding this four-carat octahedral diamond (white area, upper right), the largest recovered from a kimberlite drill core, were “astronomical,” researchers say. It was discovered in Quebec in 2003.

Diamonds, long thought to be plentiful in only a few locations, could turn up anywhere, perhaps even in your own backyard — so long as your area has some volcanic history. That’s according to a controversial model describing how diamonds are transported from Earth’s mantle to its surface.

Most of Earth’s diamonds have been found in or around kimberlite pipes, which are vertical, hollow wedges of igneous rock that extend deep into Earth, ending as a surface crater covering between 0.5 to 150 hectares (about 1.5 to 370 acres). Exploration geologists have long sought out such pipes so that miners can set up shop and extract the precious stones found inside (see Geotimes, April 2006). Researchers know that kimberlite pipes are the vehicle through which diamonds travel from their birthplace deep in Earth’s mantle to its surface, but the process by which the pipes form and transport their precious cargo has been debated since the first confirmed diamond discovery along Africa’s Orange River in the mid-1860s. Now, Lionel Wilson, a volcanologist at Lancaster University in the United Kingdom, and James Head III of Brown University in Providence, R.I., have provided a new hypothesis, published May 3 in Nature, for how the process might work.

Kimberlite pipes form from a deep volcanic eruption, but how remains a mystery. “We’ve never seen them erupt,” explains Kelly Russell, a volcanologist at the University of British Columbia in Vancouver, as the youngest-known kimberlite pipes are on the order of tens of millions of years old. Some theories suggest a complex procedure in which magma, driven by volatiles, slowly builds kimberlite chambers as it moves up through fractures in the rock toward Earth’s surface. There, pressure changes cause a downward explosion. Others suggest that rising magma must come into contact with subsurface water, creating a reaction that fragments and expands the magma explosively. But questions remain, such as how diamonds survive the rough trip through extreme changes in pressure and temperature without decomposing into graphite.

Wilson and Head arrived at a solution to the diamond conundrum while studying a curious phenomenon on the moon. During the Apollo 17 mission in 1972, geologist and astronaut Harrison Schmitt noted that the moon’s surface was littered with small glass spheres, the origin of which has since been debated. Wilson and colleagues concluded that volcanic eruptions on the moon could transport rocks from the depths of the moon to its surface, exploding with a shower of glass spheres.

Applying this same context to kimberlites works as follows: High-pressure carbon dioxide gas bubbles in the rising magma propel it up toward Earth’s surface. Pressure changes and gas expansion at the surface send a shock wave down through the bubbles, effectively popping them, causing the rock and magma to explode. The magma quickly chills, freezing the new kimberlite pipe in place along with any diamonds that traveled up with the magma.

“The key is the timing,” Wilson says, as the entire process of magma transport from mantle to surface takes place very quickly, within an hour. This short timeframe prevents diamonds from becoming unstable and disintegrating into graphite.

Wilson and Head’s hypothesis looks at the big picture of how volcanism could be involved with kimberlite pipe formation and this approach has spurred discussion, Russell says. People in the petrology and geochemistry fields might balk at the hypothesis, which “glossed over a bunch of details,” Russell says, such as why some kimberlite pipes have multiple eruption phases. But some details might be “worth glossing over,” he says, in order to rethink questions of how the magma ascends, how explosive it is and for how long it erupts.

Tom McCandless, a hydrothermal geochemist and chief mineralogist for Ashton Mining of Canada Inc. in Vancouver, says that the model is “fairly reasonable” in its attempt to explain the process. The main weakness, he says, is the depth at which the team says the carbon dioxide bubbles would form, where conditions in deep Earth would require that it remain in the liquid phase. Still, the model’s “biggest contribution” is that it employs fluids from deep in the mantle to drive the eruption.

If true, the hypothesis could have implications for where diamonds on Earth could be found. Previously, without a clear model of kimberlite formation, people have looked for diamonds in regions where the mineral has previously turned up, such as in South Africa and, more recently, in Canada’s Northwest Territories. Kimberlites have been found in these places because Earth’s crust is old enough such that the pipes have not been obliterated by geologic processes, such as plate tectonics. But the new model suggests that kimberlites get their start at depths “where [diamonds] know absolutely nothing about the Earth’s surface,” Wilson says. “Our feeling is these things could pop up anywhere.”

Kathryn Hansen

"Diamonds Bedazzle Canadian North," Geotimes, April 2006

Back to top

Ubiquitous and useful, talc is a mineral mined in more than 40 countries and distributed and used worldwide. U.S. Geological Survey (USGS) Talc Commodity Specialist Robert Virta and USGS Talc Resource Specialist Brad Van Gosen prepared the following information about talc.

When most people think of talc, they probably think of talcum and baby powder. However, these uses of talc are quite minor compared to its wide variety of applications in manufacturing. The leading use of talc is in the production of ceramics, where it acts as a source of magnesium oxide, serves as a flux to reduce firing temperatures and improves thermal shock characteristics of the final product.

Talc is a hydrous silicate composed of magnesium, silicon, oxygen and water. Although relatively pure in composition, talc can contain small amounts of aluminum, iron, manganese and titanium, which can give it a range of colors, from white, to apple green, to dark green or brown. Composed of weakly bonded microscopic platelets, talc is the softest mineral known.

The physical and chemical properties that make talc commercially useful include chemical inertness, fragrance retention, high dielectric strength, high thermal conductivity, low electrical conductivity, oil and grease adsorption, high purity, softness and whiteness. In addition to ceramics, talc is used in cosmetics, paint, paper, plastics, roofing, rubber and a variety of other materials.

In cosmetics, talc imparts softness and lubricity to products, improves blemish coverage, retains fragrances and improves oil adsorption. In paint, talc improves the hiding properties of paint, strengthens the paint film, smoothes ridges left during brush applications, helps prevent settling of components in the paint can and improves corrosion resistance for painted metals. Talc is used in paper to adsorb tree sap, thereby preventing blemishes, filling interstices between cellulose fibers, reducing paper transparency and improving ink receptivity.

In plastics, talc reduces the amount of expensive resins required in the product, improves dimensional stability, reduces permeability of plastic films, improves flexibility and strength of the plastic product, and improves heat resistance. Talc also acts as a lubricant in the plastic molding machines. For roofing, talc increases the viscosity of the bitumen, improves weathering characteristics of the product and prevents sticking of asphalt-saturated felts and shingles.

Talc is used in rubber as filler to reduce the amount of expensive resin required, increases stiffness of uncured rubber compounds, improves rigidity in the product, and acts as a lubricant and anti-stick agent in manufacturing. In adhesives and caulks, talc controls viscosity, reduces film permeability and reinforces the adhesive film. Talc also is used in agricultural applications as a chemical carrier for herbicides and pesticides or as a fruit dusting agent.

In the United States, talc is mined in six states, with Montana being the leading producer, followed by Texas, Vermont, New York, Virginia and Oregon. In 2006, U.S. production was estimated to be 880,000 metric tons of crude talc ore valued at $25 million. Domestic sales were estimated to be 861,000 metric tons, valued at $75 million. In 2006, U.S. manufacturers also used 310,000 metric tons of imported talc.

World production of crude talc ore in 2006 was estimated to be about 6.5 million metric tons. The leading producer was China with 3 million metric tons, followed by the United States with 880,000 metric tons, Finland with 550,000 metric tons, India with 545,000 metric tons, Brazil with 401,000 metric tons, and France with 350,000 metric tons. These six countries accounted for an estimated 88 percent of world talc production in 2006.

For more information on talc, visit

Back to top


Advertise in Geotimes

Geotimes Home | AGI Home | Information Services | Geoscience Education | Public Policy | Programs | Publications | Careers

© 2022 American Geological Institute. All rights reserved. Any copying, redistribution or retransmission of any of the contents of this service without the express written consent of the American Geological Institute is expressly prohibited. For all electronic copyright requests, visit: