Rock Tales from Norway

I get asked quite often what a mineralogist does for the Canadian of Museum of Nature. The answer is… a bit of everything! But most days, I spend my time focused on the world at an atomic level: collecting X-ray diffraction data to understand the atomic crystal structure of a mineral, or collecting electron microprobe or laser data to determine a mineral’s chemistry. And much of my time is spent at my computer, crunching and manipulating data or writing manuscripts for professional journals.

Once in a while, however, I have to leave the atomic world behind and refocus on the bigger picture. And what better place to do this than in the Oslo fjord region in Norway! Norway is a beautiful country, reminiscent of New Brunswick, or northern Ontario with an ocean—it has deep fjords stretching into the North Sea, extensive forests of beech and pine, fields of potatoes, onions, carrots and oats, steep cliff faces and a rocky coastline studded with fishing villages.

Paula Piilonen in an open pit mine.

Paula Piilonen at the Klåstad Quarry, Tjølling, Larvik. Prospecting in the quarry required careful coordination with local workers, as large equipment was in use and drilling underway at various times. Image: Glenn Poirier © Canadian Museum of Nature

Although the scenery is stunning, Glenn Poirier and I came here in July 2011 for scientific reasons: to continue a research project on the Larvik plutonic complex. (Browse the photo album of this trip on Flickr).

I first came to this area in 2003 to explore this unique geological “ring complex” about 100 km south of Oslo. In geological terms, this complex is a large igneous intrusion that was emplaced by a series of pulses of magma. These pulses often came up overlapping each other, and on the surface, appear to form concentric rings.

The main rock type found in the ring complex is a coarse-grained igneous rock called larvikite. Larvikite is quarried extensively for building and ornamental stone. If you’ve been in downtown Ottawa and have seen the building where the Natural Sciences and Engineering Research Council has its offices, you’ve seen larvikite. It has a distinctive blue schiller—a phenomenon caused by twinning of the feldspars in the rock. Larvikite has been quarried in southern Norway since the late 1800s, and in 2008 it was declared the country’s official rock.

But we weren’t in Norway to quarry larvikite for kitchen countertops at home! Glenn and I are studying the mineralogy and chemistry of minerals within alkaline pegmatites that can be found within the complex. During my previous trip to the Larvik region in 2003, I collected samples of pegmatites from within ring sections to understand the evolution of the magma from which the pegmatites formed.

Paula Piilonen collects rock specimens in the Klåstad Quarry.

Paula Piilonen sampling a white fracture-fill at the contact between larvikite and basalt in the Klåstad Quarry. Image: Glenn Poirier © Canadian Museum of Nature

This second trip has two main goals: to discover new pegmatites within the most highly evolved, youngest ring sections in the complex, and to collect larvikite samples from the entire complex. Although these whole rock samples won’t likely yield new mineral species, they will be used to study the trace-element evolution of the complex, and for age-dating of each of the ring sections.

In doing this, we’re studying a unique geological formation that has been of interest to scientists and mineralogists since the mid 1700s. In fact, it was more than 100 years ago, in 1890, that W.C. Brøgger published one of the great classics in mineralogy about the minerals of the pegmatites in southern Norway. He discussed the formation of the Oslo region and provided detailed descriptions of many of the pegmatites. Of the 80 mineral species that he described, 13 were new to science.

So, we are now following in his footsteps. In 10 days, we managed to collect samples from about 50 localities, enough to fill four large buckets (about 80 kg in total), which made their way across the Atlantic by container ship over the summer.

Now that the samples have arrived at my lab, the hard work begins. My research will once again refocus on using atomic-level techniques and data to understand the macroscopic world of the Larvik plutonic complex.

About Paula Piilonen

A mineralogist with the Research Division at the Canadian Museum of Nature.
This entry was posted in Fieldwork, Research, Rocks and minerals and tagged , , . Bookmark the permalink.

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