Tag Archives: silicate

This diamond contains the first evidence of calcium silicate perovskite found in nature. Credit: Nester Korolev, UBC.

Tiny diamond provides first evidence of Earth’s fourth most abundant mineral

This diamond contains the first evidence of calcium silicate perovskite found in nature. Credit: Nester Korolev, UBC.

This diamond contains the first evidence of calcium silicate perovskite found in nature. Credit: Nester Korolev, UBC.

Calcium silicate perovskite (CaSiO3) is widely regarded as the fourth most abundant mineral on Earth but it was only recently that people were able to actually see it intact. That’s because the mineral is thought to form deep inside Earth’s mantle, an area below the planet’s surface, but above the planet’s core. Only after it made its way to the surface, trapped inside a diamond recovered from a South African mine, did we get confirmation that this mineral even exists in a stable form. As such, it provides valuable insight into the processes that govern Earth’s interior.

First time found in nature

“Nobody has ever managed to keep this mineral stable at the Earth’s surface,” said Graham Pearson, a professor in the University of Alberta’s Department of Earth and Atmospheric Sciences, in a statement.

“The only possible way of preserving this mineral at the Earth’s surface is when it’s trapped in an unyielding container like a diamond,” he explained. “Based on our findings, there could be as much as zetta tonnes (1021) of this perovskite in deep Earth.”

The lucky diamond was excavated from South Africa’s Cullinan mine, where incidentally the world’s largest diamond was also found back in 1905. This goes to show that Cullinan is not only a source for material riches but also scientifically valuable, as it provides insights into Earth’s deep core.

“Being the dominant host for calcium and, owing to its accommodating crystal structure, the major sink for heat-producing elements (potassium, uranium and thorium) in the transition zone and lower mantle, it is critical to establish its presence,” the authors wrote in the journal Nature. 

Most diamonds form 150 to 200 km below Earth’s surface, but Pearson says the perovskite-containing diamond likely formed some 700 km (435 miles) deep. The scientist thinks the diamond must have sustained 24 billion pascals of pressure — or 240,000 more than the average at sea level.

This important discovery once again highlights diamonds’ important role in preserving material and revealing clues about some of the most mysterious geological processes. The calcium silicate perovskite inclusion — perhaps the first intact sample of this material that we know of — was confirmed with X-ray and spectroscopy tests.

“Diamonds are really unique ways of seeing what’s in the Earth,” Pearson said. “And the specific composition of the perovskite inclusion in this particular diamond very clearly indicates the recycling of oceanic crust into Earth’s lower mantle. It provides fundamental proof of what happens to the fate of oceanic plates as they descend into the depths of the Earth.”

Previously, in 2014, Pearson was behind another milestone discovery which found the first evidence of ringwoodite — Earth’s fifth most abundant mineral — in another diamond.

Scientific reference: F. Nestola et al, CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle, Nature (2018). DOI: 10.1038/nature25972.

Using rocks for farming could improve soil quality, reduce CO2 emissions

Adding minute rock pieces to soils can release important soil nutrients and also suck up significant quantities of carbon dioxide.

Destruction and rebirth

Fields of green: volcanic soils often host rich, lush vegetation, as can be seen in this photo of Oahu. Image credits: Jason Jacobs / Flickr.

Since the dawn of mankind, humans have tried to find ways to improve agricultural yield — a goal still sought after today. With the global population set to reach 9.7 billion by 2050, researchers are looking for better ways to safely feed the world. Now, an innovative study by University of Sheffield researchers reports an unexpected way through which we can improve production, while also helping reducing carbon dioxide emissions: using rocks as fertilizers.

The idea is that adding fast-reacting silicate rocks to croplands could capture CO2 and give increased protection from pests and diseases. In time, this process would also restore soil structure and fertility, protecting against erosion.

Professor David Beerling, lead author of the research, explains.

“Human societies have long known that volcanic plains are fertile, ideal places for growing crops without adverse human health effects, but until now there has been little consideration for how adding further rocks to soils might capture carbon.”

Volcanic eruptions can be devastating — they destroy everything in their wake, burying surroundings in a blanket of hot ash. But in the long term, volcanic deposits can develop into some of the richest agricultural lands on earth. Take the soils in Italy, for example. The southern parts of the country feature dry, limestone-rich soils. But if you move towards the north, particularly around Naples, the soils are much more fertile — largely due to the eruptions of Mount Vesuvius. Similarly, volcanic areas like New Zealand or Hawaii often feature rich, lush vegetation.

This isn’t anything new. What Beerling is proposing, however, is taking crushed, small carbon-rich rocks (such as basalt) and using them to fertilize agricultural soils. As these minute pieces dissolve in the soil, they would take in carbon dioxide and eliminate nutrients.

The destruction once caused by volcanoes could be used to inject new life into soils.

Two birds with one stone

“The magnitude of future climate change could be moderated by immediately reducing the amount of CO2 entering the atmosphere as a result of energy generation. Adopting strategies like this new research that actively remove CO2 from it can have a massive impact and be adapted very quickly,” Beerling adds.

Of course, this could be applied to all types of soils for the purpose of absorbing CO2, but to take full advantage of the process, it would be best applied over arable land. This would not only absorb CO2 but also improve soil quality and reduce the need for pesticides.

The good thing about this approach is that it would work with a wide variety of rocks — the more calcium-rich, the better. However, the fastest weathering volcanic rocks are not suitable, Beerling told ZME Science in an email.

“The approach work would work best with basic silicate rocks, richer in magnesium and calcium, that weather faster and therefore capture more CO2. But as we point out the paper, the fastest weathering basic rocks — called ultramafics – are typically enriched in metals that can be toxic so you wouldn’t want to use them on croplands.”

Even better, many areas already spread crushed limestone over arable land to reverse acidification of soils caused by farming practices, including the use of fertilizers. So the machinery and infrastructure for the practice already exists — all that needs to be done is change the rock type.

“Crushing technology is common in the mining industry,” Beerlong added in our correspondence. “The size is the particles is a crucial determinate of the rate of chemical reactions. Small particles with a high surface area react faster. Limestone — essentially calcium carbonate — reacts very fast but more often than not releases carbon dioxide rather than sequesters it.”

Professor Stephen Long at the University of Illinois Champaign-Urbana, and co-author of the study, commented:

“Our proposal is that changing the type of rock, and increasing the application rate, would do the same job as applying crushed limestone but help capture CO2 from the atmosphere, storing it in soils and eventually the oceans.”

Long also notes that people don’t understand the full extent of climate change, and scientists haven’t been truly effective in communicating these issues. He added:

“Global warming is a problem that affects everyone on the planet. Scientists generally have done a poor job of getting across the point that the world must reduce emissions of greenhouse gases from fossil fuels and combine this with strategies for extracting carbon dioxide from the atmosphere to avoid a climate catastrophe.”

The research focus now is to see how much carbon dioxide the approach would capture, how much rock is required, and how much energy is required to crush and distribute the rock, researchers say. They also want to assess the long-term impact the treatment has on soils and watercourses.

 

For the first time, researchers discover true color of distant planet

The world, known as HD189733b, has a deep azure hue, probably the result of molten silicate glass rain in the atmosphere, which scatters blue light.

blue planet

The giant planet is one of the closest and most studied in the exoplanets recently discovered; it is a sauna, a hazy hothouse swept by blow-torch winds powered by the molten silicates. It is most likely what astrophysicists call a “hot Jupiter” – a planet which originally was very similar to Jupiter, both in terms of composition and distance to its star, but then migrated much closer to its star.

Astronomers used the Hubble’s imaging spectrograph and measured both the light emitted by the star which it orbits, and the light reflected by the planet. To isolate the planet’s light, they substracted one from the other, though the process is not nearly as simple as it sounds.

“We inferred the color,” said astrophysicist Tom Evans at the U.K.’s University of Oxford, who led the study. By knowing the wavelength, “we can imagine the color the planet would have if we could look at it with our own eyes.”

It’s estimated that the temperature on the surface of the planet is a whopping 1000 C (1832 F) with winds howling at 7000 km/h (4349 miles/h). It’s atmosphere is extremely volatile, changeable and exotic, with hazes and violent bursts of evaporation. Not the habitable paradise Earth is.

So our planet appears blue from outer space due to the oceans, which absorb red and green wavelengths more strongly than blue ones. To accentuate the effect, scattered molecules of oxygen and nitrogen in the atmosphere also selectively absorb wavelengths. Mars appears red due to its rusty surface, very rich in oxide, absorbing the blue and green wavelengths and reflecting the red ones. But the color of HD 189733b comes solely from the interplay of light in its super-heated atmosphere.

The fact that astronomers were able to measure this is a stunning achievement in itself.

“We are really pushing the limits of what we can measure,” said Mr. Evans.