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petrology

Imaggeo on Mondays: A slice of fossil life

Imaggeo on Mondays: A slice of fossil life

I am a petrographer at the University of Padova, Italy, studying the metamorphic rocks that form the deep Earth’s crust beneath our feet, and what happens when they get so hot to start to melt.

I’ve spent (enjoyed I should say) more than 30 years looking at rocks with an optical microscope. This simple, cheap tool, and more importantly, its skilled use, remain key ingredients for good research in petrology!

I’ve been taught by scientists, like Ron Vernon of Macquarie University in Australia, that a good micrograph is essential to document my research and strengthen my conclusions, and so I’ve always paid particular attention to the quality of photos. In the meanwhile, I have also developed a particular interest in photomicroscopy with an aesthetic purpose, realizing that the cocktail of rocks and polarized light has an extraordinary potential in the ‘sciart’ (Science-and-Art) field.

The digital revolution has marked a turning point in this activity, and 10 years ago I have started my micROCKScopica project to showcase to the public the beauty hidden in the small slices of rock that are thin sections.

When I find a photogenic rock I play with polarizers to get the desired combinations of color, and then I take a photograph. And people can enjoy the images, their colors and shapes, even without knowing the geological history behind them.

This is particularly true for this photograph: it is a thin section of a piece of dinosaur bone but I don’t know much about it (what bone, which dinosaur), only that it had been collected in Utah, in the United States. I received a small sample of the bone by Denise M. Harrison, a friend with whom I collaborated for a book on Lake Superior Agates. She is an award-winning lapidary (someone who cuts, polishes and engraves stones), and makes lovely cabochons with all sort of semiprecious, hard stones. I asked her for some leftovers to make some thin sections, because I wanted to see something new, possibly silicified (impregnated with silica during fossilization) because chalcedony – the very fine-grained variety of common quartz – may be extremely photogenic.

I had no idea of how a bone could look like under the microscope, and the first sight left me speechless! The porous structure, and the patterns of the radiating textures in the chalcedony fillings are extraordinary, and provide a wealth of possibilities for nice images.

In this shot, that I replicated in red and blue, a larger hole had been filled with a fine-grained quartz sand – the dark moon shape on top left – somehow interrupting the regular pattern of the bone tissue, that to someone may recall Australian Aboriginal artwork.

Curiously, this anatomically-related image made me quite popular among pathologists and other medical doctors, who find many analogies with their subjects of research. The ages of the specimens are some hundred million years apart, though…

By Bernardo Cesare, University of Padova, Italy

www.microckscopica.org

Editor’s note: The fossil sample featured in this photo was collected and distributed legally from Utah.

If you pre-register for the 2019 General Assembly (Vienna, 07–12 April), you can take part in our annual photo competition! From 15 January until 15 February, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Quartz lawns and crystal flowers

Petrologists spend a large part of their time peering down microscopes at wafer thin slices of rock to work out what they’re made of and how they were formed. What lies on the other side of the lens can be an incredibly beautiful pattern, a kaleidoscope of colour, or stark bands of black and white, all of which provide clues to the rock’s history, and the history of the landscape it came from. Bernardo Cesare, enthusiastic photographer and professor of petrology at the University of Padova, Italy, has captured some fantastic images of these slender rock sections, including the incredible image of ocean jasper, below.

Ocean jasper under the microscope – 30 micrometres thin and almost entirely quartz. (Credit: Bernardo Cesare via imaggeo.egu.eu)

Ocean jasper under the microscope – 30 micrometres thin and almost entirely quartz. (Credit: Bernardo Cesare via imaggeo.egu.eu)

Ocean jasper is a variety of jasper found only in Madagascar and is increasingly sought after as a precious stone, and with that, decent rock samples are hard to come by. “I have long been searching for affordable samples of ocean jasper, until I saw a necklace in a market stall. I cut all the beads, prepared thin sections from them, and put them under the microscope,” says Cesare.  “They turned out to contain a microscopic garden of quartz flowers in a fine-grained silica matrix. In places some coarser crystals form ‘rosettes’ in a lawn of fibrous quartz too.”

Jasper jewelery – it looks even more lovely under the microscope, don’t you think? (Credit: Tess Norberg/Nova Design)

Jasper jewellery – it looks even more lovely under the microscope, don’t you think? (Credit: Tess Norberg/Nova Design)

Ocean jasper is made up of many minute orbs, just a few millimetres in diameter, known as spherulites. They form when silica-rich volcanic rocks change from being glassy to crystalline, and are saturated with silica in the process. This crystallisation occurs in arrays of thousands of fibrous, needle-like crystals. “They can grow as perfect spheres, but where they’re too close to one another the growing spherulites impinge on each other,” Cesare explains. This close clustering causes the spherulites to have sharp boundaries where they meet, something clearly seen in Cesare’s snap of the crystal structure.

Even though almost everything in the image (the exception being the small black dots, which are opaque minerals) is made of quartz, a rainbow of colours can be seen. These rainbows are known as interference colours, and they appear when polarized light passes through a crystal. So what creates this rainbow?

When white light, first polarized by a filter, passes through the crystals of a rock, it is split in two components that travel at different speeds. These components interfere with the crystal structure in different ways depending on their wavelength and the crystal’s orientation. When light emerges from the crystal and is filtered for the second time, some wavelengths are suppressed, so the colour of the light is no longer white. Cesare explains why: “the interference colour depends on the type of mineral (more precisely on its birefringence), on its thickness, and on its orientation. This is why crystals of the same mineral (quartz) may display different colours in my image: because they have different optical orientations!”

There are even ways to test out this tool at home: “even without a slice of rock, readers can test how interference colours emerge using two “crossed” polarizing filters (for example two orthogonal lenses of some sunglasses) and placing a stretched piece of plastic bag between them,” says Cesare.

A shiny sample of ocean jasper (Credit: Druzy Macro)

A shiny sample of ocean jasper (Credit: Druzy Macro)

“Polarized light is one of the fundamental tools of a geologist: with a polarizing microscope and a thin section we can recognize different minerals without the aid of more sophisticated and expensive analyses. Looking at colours and at their changes, at the shapes and contours of mineral grains, at their sizes and mutual relationships, not only can we understand which minerals a rock contains, but also in which sequence they formed, if some deformation occurred during or after their crystallisation, if they were transformed into other minerals and, qualitatively, at which pressure and temperature conditions the rock originated or evolved.” All these observations form the basis for more detailed research, such as, working out how many millions (or billions) of years ago the rock formed.

You can find out more about ocean jasper and Cesare’s photographic style over at National Geographic and on Geology In Art. You can also find more of his photography over at www.microckscopica.org.

By Sara Mynott, EGU Communications Officer

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Scope for science and art

Great geoscience photographs aren’t always shots of beautiful landscapes. Sometimes there are stunning things to see at a much smaller scale. This week’s Imaggeo on Mondays showcases one such curiosity and highlights how research images can reveal a lot about the natural world when exhibited as a form of art.

Thin sections are a fantastic way of finding out more about rocks, soils and tissue structure. At 30 micrometres thick they are the most refined Carpaccio you could find on a geoscientist’s plate, and illuminating them under a microscope only makes the sections more splendid.

A sandstone sample viewed in plane polarized light (top) and cross polarised light (bottom). (Credit: Wikimedia Commons user Michael C. Rygel)

A sandstone sample viewed in plane polarised light (top) and cross polarised light (bottom). (Credit: Wikimedia Commons user Michael C. Rygel)

Under plane polarised light, you spot the fine details that make up each slice, the crystal grains, pore spaces and shell fragments that, together, make up your rock sample. And in cross polarised light there’s even more to be seen. Crystals, at first barely perceptible, shine out amid dark masses and appear as an array of bright and beautiful colours. Different properties like the refractive index and extinction of a crystal can let you work out what mineral you’re looking at, and the relationships between mineral grains offer clues to the rock’s history.

Under the microscope, where mineral and biological worlds meet. (Credit: Laura Gargiulo via imaggeo.egu.eu)

Under the microscope, where mineral and biological worlds meet. (Credit: Laura Gargiulo via imaggeo.egu.eu)

This image, by Laura Gargiulo, shows the surface of a sandy soil under cross polarised light. Sand grains – a veritable pick a mix of rock fragments and merged minerals – make up the majority and a slice of cellular plant material sits just south of the centre. Each of the colours and the way they change under polarised light reveal what each sand grain is made of and how these tiny fragments combine to make up the soil. While its purpose may be a scientific one, the image certainly has aesthetic appeal.

By Sara Mynott, EGU Communications Officer

If you are pre-registered for the 2014 General Assembly (Vienna, 27 April – 2 May), you can take part in our annual photo competition! Up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.