Earth Magnetism and Rock Physics

MinCup: Elevating humble minerals to new heights

MinCup: Elevating humble minerals to new heights

Throughout October and November, the world of (Earth science) Twitter was taken by storm: Day after day, Eddie Dempsey (a lecturer at the University of Hull, and @Tectonictweets for those of you more familair with his Twitter handle) pitted minerals against each other, in a knock out style popular contest. The aim? To see which mineral would eventually be crowned the best of 2017.

Who knew fiery (but good natured) rows could explode among colleagues who felt, strongly, that magnetite is far superior to quartz or plagioclase? The Mineral Cup hashtag (#MinCup) was trending, it was in everyone’s mouth. Who would you vote for today?

What started as a little fun, became a true example of great science communication and how to bring a community of researchers, scattered across the globe, together.

And then Hazel Gibson (former EGU Press Assistant, @iamhazelgibson) came along. She was an active participant in the competition, but also contributed beautiful sketches of every mineral featured, and shared them for all to see by tagging them with the #MinCup hashtag. We all know that a picture is worth more than a thousand words, so when Hazel’s hand drawn sketches where paired with an already rocking contest, it’s impact and reach was truly cemented.

Between them, Eddie and Hazel had managed to elevate the humble mineral to new heights.

Why do minerals matter?

Minerals are hugely underrated. They are often upstaged by the heavy-weights of the geosciences: volcanoes, earthquakes, hurricanes, fossils and melting glaciers (to name but a few).

But they shouldn’t be.

Minerals are the building blocks of all rocks, which in turn, are the foundation of all geology.

Whether you study the processes which govern how rivers form, or ancient magnetic fields, or fossils, chances are your work will, at some stage, involve looking at, studying, or at the very least understanding (some) minerals. Mineralogy 101 (or whatever it’s precise name was at your university) is a rite of passage for any aspiring Earth scientist. I still remember hours spent painstakingly looking down a microscope, drawing and annotating sketches trying to decipher the secrets of the Earth’s ancient past, locked in minerals.

And that’s just the beginning.

Minerals are of huge economic and, therefore societal importance, too. Many minerals are vital ingredients in house-hold products and contribute to the manufacturing processes of many others. Yet, they fail to make headlines and their true significance, often, goes unnoticed.

So, in hopes to further highlight the relevance and importance of minerals, I’ve picked a few of the #MinCup minerals and explained why they (should) matter (to you).


Gypsum will form in lagoons, where ocean waters are high in calcium and sulfate content, and where the water evaporates slowly overtime. In rocks, it is associated with sedimentary beds which can be mined to extract the mineral, but it can also be produced by evaporating water with the right chemical composition.

Gypsum has been used in construction and decoration (in the form of alabaster) since 9000 B.C.  Today, it has a wide variety of common uses. Did you know that many fruit juice companies use gypsum to aid the extraction of the liquid? It is also used in bread and dough mixes as a raising agent. And it’s uses aren’t limited to just the food and drink industry. It is also commonly used as a modelling material for tooth restorations and helps keeps us safe when added to plastic products where it acts as a fire retardant.


Geologically speaking, magnetite holds the clues to understand the Earth’s ancient magnetic field. Credit: Hazel Gibson

Typically, greyish black or black, magnetite is an important iron ore mineral. It occurs in many igneous and volcanic rocks and is the most magnetic of all minerals. For it to form, magma has to cool, slowly, so that the minerals can form and settle out of the magma.

Due to its magnetic nature, it has fascinated human-kind for centuries: it paved the way for the invention of the modern compass.  The iron content in magnetite is higher than its more common cousin haematite, making it very sought after. Iron ore is the source of steel, which is used universally throughout modern infrastructure.

Geologically speaking, magnetite holds the clues to understand the Earth’s ancient magnetic field. As magnetite-bearing rocks form, the magnetite within them aligns with the Earth’s magnetic field. Since this rock magnetism does not change after the rock forms, it provides a record of what the Earth’s magnetic field was like at the time the rock formed.


Arguably, one of the most well-known of the minerals, diamond is unique, not only for its beauty and the high prices it reaches, but also for its properties. Not only is it the hardest known mineral, it is also a great conductor of heat and has the highest refractive index of any mineral.

Though mostly sought after by the jewellery industry, only 20% of all diamonds are suitable for use as a gem. Due to it’s hardness, diamond is mined for use in industrial processes, to be used as an abrasive and in diamond tipped saws and drills. Its optical properties mean it is used in electronics and optics; while it’s conductive properties mean it is often used as an insulator too.

Diamond: perhaps the most sought after mineral of them all? Credit: Hazel Gibson


Last, but absolutely not least, let’s talk about Olivine – the winner of #MinCup 2017.

Olivine is a pretty, commonly green mineral. Because it forms at very high temperatures, it is one of the first minerals to take shape as magma cools, and given enough time, can form specimens which are easily seen with the naked eye. Changes in the behaviour of seismic waves as they traverse the Earth indicate that Olivine is an important component of the Earth’s inner layer – the Mantle.

It’s a relatively hard mineral, but overall hasn’t got highly sought-after properties and, as result, has been used rather sparingly in industrial processes. In the past it has been used in blast furnaces to remove impurities from steel and to form a slag, as well as a refractory material, but both those uses are in decline as cheaper materials come to the market.

Perhaps better known is its gemstone counterpart: peridot, a magnesium rich form of Olivine. It has been coveted for centuries, with some arguing that Cleopatra’s famous ‘emeralds’, where in fact peridote. Until the mid-90s the US was the major exporter of the gem stones, but deposits in Pakistan and China now challenge the claim.

So, do you think Olivine was the rightful winner of #MinCup 2017? With a new edition of the popular contest set to return in 2018, perhaps it’s time to shout about the properties and uses of your favourite mineral from the roof tops? Not only might it ensure it is crowned winner next year, but you’ll also be contributing to making the value of minerals known to the wider public. Heck! If you’d like to tell us all about the mineral you think should be the next champion, why not submit a guest post to GeoLog?

In the meantime, if you haven’t already got your hands on one, Hazel tells me there are a few of her charity #MinCup 2017 calendars up for grabs, so make sure to secure your copy – and contribute to a good cause at the same time.

By Laura Roberts Artal, EGU Communications Officer

Imaggeo on Mondays: Smoking mountain top

Imaggeo on Mondays: Smoking mountain top

Japan’s northernmost, second largest and least developed island, Hokkaido, is famous for its unspoilt nature. Harsh, cold and snowy winters make way for pleasant summers, which allow tourists and locals to enjoy a variety of outdoor activities, year-round, in the island’s six protected areas.

The largest of the natural parks is Daisetsuzan: known for it’s wilderness and volcanoes. It is formed by the Daisetsuzan volcanic group, which is arranged around the Ohachidaira caldera. The highest peak of the group is Mt. Asahidake (2,291 m above sea level) and remains active. The Mt. Tokachi volcanic group, named after its highest peak Mt. Tokachi (also an active volcano), and the Ishikari Mountain Range, which includes the Mt. Shikaribetsu volcanic group near Lake Shikaribetsu and older geological strata of the Hidaka Mountain Range, make up the rest of the volcanic groups in the park.

Mt. Asahidake has not erupted since 1739, but constantly releases steam, which escapes from cracks across it’s volcanic slopes. According to Daniela Domeisen, who took the photograph we feature today:

“The fumaroles give the volcano its characteristic look and sulphuric smell.”

She goes on to describe the impressive volcanic setting:

“The mountain raises rather slowly, but with a steep and slippery peak. The descent on the opposite side is literally a secluded paradise, with the soil and the plants competing for the most beautiful patchwork of colour.”

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


GeoSciences Column: Don’t throw out that diary – medieval journals reveal the secret of lightning

GeoSciences Column: Don’t throw out that diary – medieval journals reveal the secret of lightning

When 17th century Japanese princess Shinanomiya Tsuneko took note of an afternoon storm in her diary one humid Kyoto summer, she could not have imagined her observations would one day help resolve a longstanding scientific conundrum. Statistical analysis of her journals has revealed a link between lightning strikes and the solar wind – proving that your teenage diary could contain good science, as well as bad poetry.

The mystery of lightning

Lightning has amazed and alarmed weather-watchers since time immemorial. So it may come as a surprise that we still have little idea what sets off one of nature’s most thrilling spectacles.

Any school child will tell you lightning is caused by a difference in electrical charge. Up- and downdrafts cause molecules of air and water to bump against each other, exchanging electrons. When the potential difference is big enough, all those separated charges comes rushing back in one big torrent, superheating the air and turning it into glowing plasma – that’s what we call lightning.

So far, so sensible. But there’s a problem. Air is an insulator – and a very good one at that. To get the current flowing, charged particles need some sort of bridge to travel across. And it’s this bridge that has vexed lightning scientists – fulminologists – for decades.

The most prominent theory points the finger at cosmic rays – heavy, fast-moving particles that impact the Earth from space. Packing energy roughly equivalent to a fast-bowled cricket ball into one tiny atom-sized package, a cosmic ray can shred electrons from their nuclei with ease. The spectacular Northern Lights reveal the effect this can have on the atmosphere: columns of ionised air, perfect conductors for charges to travel along.

Most cosmic rays originate in deep space, hurled at close to the speed of light from distant supernovae. The extreme heat of the sun’s surface also sends more than a few our way – the so-called ‘solar wind’ – but because these particles are more sluggish than galactic cosmic rays, researchers at first doubted they could have much effect on the atmosphere. Lightning’s time in the sun was yet to come.

27 days of summer

Anyone who has lived a year in Japan will be familiar with the country’s long, sultry summers – and its famously methodical Met Agency. It’s a good place to go looking for lightning.

Inspired by some tantalising work out of the UK, Hiroko Miyahara and colleagues across Japan went sifting through their own Met data for patterns that might suggest a connection between solar weather and lightning strikes. They had their eye out for one pattern in particular – the 27-day cycle caused by the sun’s rotation. This is just short enough that the solar wind streaming from any given region of the sun is fairly constant, limiting the impact of solar variability on the data. It’s also short enough to fit comfortably within one season, which helped the authors compare apples with apples over long timespans.

Armed with the appropriate controls, and a clever method they developed for counting lightning strikes that smooths over patchy observations, Miyahara and the team got stuck into the data for Japan circa 1989–2015. Early in 2017, in a paper published in Annales Geophysicae, they presented their results. The 27-day signal stood out to four standard deviations: a smoking-gun proof that solar weather and lightning strikes are connected.

But how is the relatively sluggish solar wind able to influence lightning strikes? The key, according to Miyahara, is the effect the solar wind has on the Earth’s magnetic field – sometimes bolstering and sometimes weakening it, allowing the more potent galactic cosmic rays to wreak their mayhem.

A window into the past

Of course, the 27-day cycle is only the shortest of the major solar cycles. It is well known that the intensity of the sun varies on an 11-year cycle, related to convection rates in the solar plasma. Less understood are the much longer centurial and millennial cycles. The sun passed through one such cycle between the late Middle Ages and now. The so-called Little Ice Age, coinciding with a phase of low sunspot activity known as the Maunder Minimum, precipitated agricultural collapse and even wars across the world – and solar physicists believe we may be due for another such minimum in the near future, if it hasn’t begun already.

Understanding these cycles is a matter of no small importance. Unfortunately, pre-modern data is often scattered and unreliable, hampering investigations. A creative approach is called for – one that blends the disciplines of the human historian and the natural historian. And this is exactly what Miyahara and the team attempted next.

Shinanomiya Tsuneko was born in Kyoto 1642 – just before the Maunder Minimum. A daughter of the Emperor, Shinanomiya became a much-respected lady of the Imperial Court, whose goings-on she meticulously recorded in one of the era’s great diaries. Luckily for Miyhara and his colleagues in the present day, Shinanomiya was also a lover of the weather, carefully noting her observations of all things meteorological – especially lightning.

Figure and text from Miyahara et al, 2017b: “a) Group sunspot numbers around the latter half of the Maunder Minimum. b) Solar cycles reconstructed from the carbon-14 content in tree rings. The red and blue shading denotes the periods of solar maxima and minima, respectively, used in the analyses. c) Periodicity of lightning events during the solar maxima shown in panel (b). The red dashed lines denote 2 and 3 SD during the solar maxima, and the red shaded bar indicates the 27–30-day period. d) Same as in panel c) but for solar minima.”

Shinanomiya’s diary is one of five Miyahara and the team consulted to build a continuous database of lightning activity covering an astonishing 100 years of Kyoto summers. Priestly diaries, temple records, and the family annals of the Nijo clan were all cross-referenced to produce the data set, which preserves a fascinating slice of Earth weather during the sun’s last Grand Minimum.
Analysis of this medieval data revealed the same 27-day cycle in lightning activity observed in more recent times – proof of the influence of the solar wind on lightning frequency. The strength of this signal proved to be greatest at the high points of the sun’s 11-year decadal sunspot cycle. And the signal was almost completely absent between 1668 and 1715 – the era of the Maunder Minimum, when sunspot numbers are known to have collapsed.

Put together, the data provide the strongest proof yet that solar weather can enhance – and diminish – the occurrence of lightning.

Lightning strikes twice

Miyahara and the team now hope to expand their dataset beyond the period 1668 – 1767. With a little luck – and a lot of digging around in dusty old archives – it may be possible to build a record of lightning activity around Japan from before the Maunder Minimum all the way up to the present day. A record like this, covering a grand cycle of solar activity from minimum to maximum and, perhaps soon, back to a minimum again, would help us to calibrate the lightning record, providing a powerful new proxy for solar activity past and future. It may even help us to predict the famously unpredictable – lightning strikes injure or kill a mind-boggling 24,000 people a year.

As for the rest of us, the work of Miyahara and his colleagues should prompt us to look up at the sky a little more often – and note down what we see. Who knows? Three hundred years from now, it could be your diary that sets off a climate revolution – though it may be best to edit out the embarrassing details first.

by Rohan S. Byrne, PhD student, University of Melbourne


Miyahara, H., Higuchi, C., Terasawa, T., Kataoka, R., Sato, M., and Takahashi, Y.: Solar 27-day rotational period detected in wide-area lightning activity in Japan, Ann. Geophys., 35, 583-588,, 2017a.

Miyahara, H., Aono, Y., and Kataoka, R.: Searching for the 27-day solar rotational cycle in lightning events recorded in old diaries in Kyoto from the 17th to 18th century, Ann. Geophys., 35, 1195-1200,, 2017b.

Imaggeo on Mondays: A spectacular view of moss-covered rocks

Imaggeo on Mondays: A spectacular view of moss-covered rocks

Geology has shaped the rugged landscape of the Isle of Skye – the largest island of Scotland’s Inner Hebrides archipelago. From the very old Precambrian rocks (approximately 2.8 billion years old) in the south of the island, through to the mighty glaciers which covered much of Scotland as recently as 14,700 years ago, the modestly-sized island provides a snap-shot through Earth’s dynamic history.

A far cry from its modern cold, foggy and drizzly weather, back in the Jurassic age (250 million years ago, or so), the island was part of hot and dry desert. Over time, the sea encroached the low-lying plain, depositing sands and muds, and later sandstones, as well as thin limestones and shales across the island. The best examples of these rocks are found on the western side of the island, on the Strathaird Peninsula, but they can also be found on northern and eastern coastal stretches too.

Fast-forward to the Tertiary period (approximately 60 million years ago) and the landscape changed dramatically. The calm tropical waters had made way for explosive eruptions, which vented lavas from crack’s in the Earth’s crust. The lavas blanketed large areas of the north of the island, covering the sediments deposited back in the Jurassic.

Long after the surface explosive activity ended, the cracks in the Earth’s crust continued to serves as pathways for molten magma to move below the surface. In the norther part of the island, the lava travelled sideways, pushing its way between the layers of Jurassic sedimentary rocks. The black lavas, layered between the lighter coloured limestones and sandstones (as pictured above), are in stark contrast with the present-day moss-covered cliffs.

The most spectacular examples of this layering of volcanic units atop sedimentary rocks can be seen not far from where this photograph was taken, at Kilt Rocks, in south Staffin. Visitors to the area can also enjoy Mealt waterfall, where water from Mealt Loch (the Scottish word for lake) tumbles spectacularly into the Sound of Raasay.

Marius Ulm, who captured today’s featured image, is a civil/coastal engineer meaning a totally different aspect of the geology captured his attention:

“From a coastal engineering point of view, what is interesting is the missing moss-cover at the cliff’s toe. There is a line which marks the transition where the rocks stop being covered by moss also indicates how high water regularly rises due to tides. It tells us the tidal range (difference between low and high water) reaches up to 5 m in this area.”

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