Category: minerals

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geology minerals scotland volcanoes

Geological field trip through Scotland: Basalts from the Isle of Skye

Robert Sturm The Isle of Skye is a part of the Inner Hebrides in the north-west of Scotland. It has a total area of 174,000 hectares and has an irregularly shaped coastline that is typical of the British Isles. Since the early nineteenth century, the island has become a centre of geological research, because rocks of different geological periods are exposed there. For instance, the gneisses of the Lewisian complex were formed in the Proterizoicum, 2,800Ma and, therefore, are some of the oldest rocks in Europe. On the other hand, intrusive and extrusive igneous rocks can be assigned to magmatic events that covered wide parts of the island during the Tertiary. This event, which took place about 60Ma, resulted in the development of the Atlantic Ocean in its present form. In more recent times, two ice ages, which affected the island 26,000 years ago (the Dimlington glacial) and 11,000 years ago (the Loch Lomond glacial), resulted in the formation of a partly spectacular glacigen landscape (a landscape formed by the ice) with sediments that are of high interest for geological research. Fig. 1. Geological map of the Isle of Skye (modified after Anderson & Dunham 1966) illustrating the high variability of rocks that can be found on the island. Impressive evidence for the Tertiary volcanism is provided by the plateau lava series (these are horizontally stacked layers of lava), mainly exposed in the north and west of the island. These extrusive rock formations probably reached a thickness of 1,200m before … Read More

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Shear zones: Natural laboratories of rock deformation and mineral alteration

Robert Sturm (Austria) During the last few decades, the interest of diverse geosciences has increasingly focussed on the examination of so-called ‘shear zones’, because the displacements between two lithological blocks represent natural ‘laboratories’, within which the phenomena of mineral alteration and deformation are clearly shown for the purposes of scientific study. Many shear zones are only a few centimetres in size, meaning that their examination is relatively easy. Others, like the San Andreas Fault, have a width of several hundreds of metres, which requires a bit more effort to investigate (Fig. 1). Fig. 1. Some selected examples of shear zones with different dimensions: (a), (b) small-scale shear zones in the Zillertal/Austria, (c), (d) medium-scale shear zone in the Bohemian Massif/Austria, and (e) the San Andreas Fault. Shear zones – definitions and main characteristics Broadly speaking, along a shear zone, two lithological units – ranging in size from several square metres to the size of continentals – are displaced against each other. The movement has to be exclusively evaluated in terms of plate tectonics and often represents the cause of earthquakes. Depending on their orientation, three main types of shear zones can be distinguished (Fig. 2): The normal fault is characterised by the lowering of a lithological block with respect to its neighbouring tectonic unit. If the face of displacement between the two blocks has only a small angle of inclination, the shearing process is accompanied by crustal extension which is most impressively seen in the Rhinegraben and the East African … Read More

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Book review: Geology of south Dorset and south-east Devon and its World Heritage Coast, The British Geological Survey

I don’t normally review BGS memoirs – they are excellent publications, but largely written for the professional or the seriously committed amateur geologist. (I have to admit to owning several, which cover my favourite fossil collecting areas of the UK.) However, this is one ‘Special Memoir’ that I am quite willing to make an exception for.

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Tauern gold: The history of gold mining in the Central Alps

Dr Robert Sturm (Austria) Exploitation of gold deposits in the Hohe Tauern, in the Central Alps of Austria, has a long history: occurrences of this noble metal were explored for the first time about 2,000 years ago. Since the fourteenth century, the search for gold has been conducted on an industrial level, resulting in the production of 130km of tunnels and shafts, with the main centres of medieval gold production being the Gastein Valley, Rauris, Heiligenblut, Fusch and, later on, Schellgaden. In the second half of the fifteenth century, all of the gold found in the Central Alps was sold to Venice, but from the year 1501, the noble metal was exclusively used for indigenous minting and, therefore, all gold mines came under the archbishop’s control. Fig. 1. Map showing the position of the Hohe Tauern National Park (green) in Austria and the main locations of historical and current gold exploration. The economic zenith of gold exploitation in the Central Alps was reached in the middle of the sixteenth century. At this time, three families – the Weitmosers, Zolts and Strassers – dominated the mining industry in the Gastein Valley and in Rauris. In 1557, 830kg of gold (corresponding to about 27,000 ounces) and 2,723kg of silver were hauled from the mines. However, 50 years later, gold mining ceased completely. The main reason for this economic collapse was the total exhaustion of all lodes of ore that had been exploited in the Hohe Tauern until that time. Furthermore, only ‘visible’ … Read More

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Cameos from Ancient Greece and Rome: Small but precious treasures

Dr Robert Sturm (Austria) When talking about precious or semi-precious gemstones, most people think of the diamonds they cannot afford or rubies, agates and similar well-known minerals. But, only a few people know that gemstones have been subjected to various carving techniques since ancient times, making from them small but marvellous works of art. Basically, the most commonly applied technique of gem carving is the so-called cameo, which, in most cases, features a raised relief and, therefore, differs from the so-called intaglio that has an engraved or negative image. Ancient cameos date back as far as the third century BC and were first produced in Greece, where they mainly served as jewellery for the Hellenistic kings and their retinues. In ancient Rome, cameos and similar works of art were highly popular, especially in the family circle of the Emperor Augustus (27 BC to 14 AD), who developed a great affection for this kind of art. Roman cameos generally continued Hellenistic styles and were marked by only very few innovations. The extremely high quality of gem carving (which will be discussed more in detail below) was maintained until the end of the second century AD, but, with the beginning of the third century AD, it was subject to a sharp decline that can also be seen in other fields of art. During the European Middle Ages, cameos were highly appreciated by the aristocracy, but, nevertheless, the production practices developed in the ancient world found their application only in very rare cases, … Read More

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Book review: Geology of the Jurassic Coast: The Red Coast Revealed – Exmouth to Lyme Regis, by Richard A Edwards; and Geology of the Jurassic Coast: The Isle of Purbeck – Weymouth to Studland, by Paul Ensom and Malcolm Turner

The Jurassic Coast Trust is certainly producing some good books these days. I have alraedy reviewed one (The Jurassic Coast: An Aerial Journey through time by Peter Sills) and I think these two might even be better. As is well known, in recognition of its wonderful geology, the coast between Orcombe Rocks in southeast Devon and Old Harry Rocks in south Dorset was granted World Heritage status in December 2001.

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Along the Chain of Craters Road, Big Island, Hawaii: Part 5

Dr Trevor and Chris Watts (UK) This is the last of five articles on the ‘Chain of Craters Road’ on Hawaii’ Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.3.7 miles: the pahoehoe flow Adjacent to the road, this is a wide-spreading series of flows dating mainly from 1969 to 1974, from Mauna Ulu. In the southern part, the lavas also originate from the smaller volcano of Mauna Loa o Mauna Ulu. These are varied, but mainly formed as thin, smooth sheets. They were often broken up after solidifying by being pushed upwards into low mounds by fresh lava invading beneath them and also by the lava beneath them draining away, causing the thin skin to collapse. The forest that existed here is now seen as tree moulds. These are generally in an excellent, fresh condition, and … Read More

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Along the Chain of Craters Road, Big Island, Hawaii: Part 4

Dr Trevor and Chris Watts (UK) This is the fourth of five articles on the ‘Chain of Craters Road’ on Hawaii’ Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.3.7 miles: Mauna Ulu A short road to the east finishes in a large car park. The trail continues eastwards through the woodland (Fig. 1) for a few hundred yards until it opens out to a view of the twin peaks of nearby Pu’u Huluhulu and the more distant, and much higher, Mauna Ulu (Fig. 2). Fig. 1. A side trail into the forest close to Mauna Ulu car park. Fig. 2. Where the trail divides left and right. The dark a’a lava spreads across the lighter ash and lapilli flow. The twin peaks form Mount Pu’u Huluhulu; the more distant low rise is the shield volcano, Mauna … Read More

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Along the Chain of Craters Road, Big Island, Hawaii: Part 3

Dr Trevor and Chris Watts (UK) This is the third of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.2.6 miles: the Hi’iaka lava field and lava tree forest This is just across the road from the Hi’iaka Crater and is the later (May 1973) lava flow. It is very extensive and is little explored beyond the first 100 yards from the road. Before the eruption, there was a forest here, mainly of ʻŌhiʻa trees, but, on 5 May 1973, a series of fissures opened up and vast amounts of lava gushed forth (Fig. 1). Spreading over several miles, it devasted the forest, filled several former collapse craters, became ponded up at the Koa’e Fault cliff, and flowed away. It drained back almost to the original surface … Read More

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Along the Chain of Craters Road, Big Island, Hawaii: Part 2

Dr Trevor and Chris Watts (UK) This is the second of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.Down the Chain of Craters Road 0.3 miles: the July 1974 flow This flow, which was mostly pahoehoe lava, covered several hectares. It came from the nearby cone of Ma’una Ulu, a subsidiary cone of Kilauea. The eruption began in May 1969 and lasted until July 1974. It featured many periods of spectacular fire fountains, including one that reached 300m high on 30 December 1969 (Fig. 1). Fig. 1. Mauna Ula fire fountain 1968. (Source: USGS.) Spreading as far as the sea, it added 94 hectares of new land to Big Island – more than 230 hectares. In addition to spreading across the surface, much lava sank, returning … Read More

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Along the Chain of Craters Road, Big Island, Hawaii: Part 1

Dr Trevor and Chris Watts (UK) This is the first of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Introduction Kilauea volcano dominates the southeast of Hawaii’s Big Island. At 1,247m high, it is by no means the biggest or highest of Hawaii’s peaks, but it is easily the most active. It doesn’t have a peak. Instead, there is a caldera – a huge, oval-shaped collapse crater that formed 500 years ago in the space of a few days – perhaps a few hours. It now measures about 5km long by 3km wide, and is 165m deep (Fig. 1). Fig. 1. Regional sketch of Kilauea’s caldera and the Chain of Craters Road. Its appearance and dimensions have changed considerably over the years as different parts of the caldera have erupted at different times and in different ways. The most spectacular event in the past century was the 600m-high, fire-fountain episode in 1959, which filled the caldera floor with a lava lake and created the ‘side caldera’ of Kilauea Iki. The main eruptive point now is the fire pit known as Halema‘uma‘u that … Read More

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The Geologists’ Association: An overview

Diana Clements (UK) The Geologists’ Association (GA) was formed in 1858 and, from its inception, was an inclusive organisation set up to embrace both professional and amateur geologists, unlike the Geological Society, some 50 years older, which was only intended for professionals. Women were accepted from the beginning – similar organisations of the time were habitually men only. It was intended as a meeting-place for like-minded people and fieldtrips were always an important part of the Associations’ activities. As early as 1895, Local Groups around the country were set up to extend activities nationwide; now we have 17 Local Groups with a further 72 other geologically-related societies that are affiliated with the GA. The aims that we adhere to now were developed gradually and foremost among them is to make geology available to a wider public. The Proceedings of the Geologists’ Association first appeared in 1859, only a year after its formation, and included written papers presented first to members at the Friday lectures and the write-ups from the early fieldtrips. These are often important historical documents of geology in a bygone age, no longer visible, particularly in urban environments. Fig. 1(a) A fieldtrip to Gilbert’s Pit, Charlton in 1913, when the quarry was operating. Fig. 1(b) The same face in 2016, with steps erected to view the remaining exposure of geological interest. As well as the images in the write-ups, the GA possesses a large archive of photographs and associated ephemera documenting the activities of the Association since the … Read More

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Book review: Hutton’s Arse: 3 billion years of extraordinary geology in Scotland’s Northern Highlands (2nd edition), by Malcolm Rider and Peter Harrison

If you can see past the somewhat robust title (a reference to James Hutton’s discomfort riding around Scotland on horseback during his geological investigations), this is an interesting read, combining both geological science and humour in just about the right measures.

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Milos: A must-visit island destination for the geo-traveller

Ken Madrell (UK) Introduction Most visitors to the Cyclades islands will gravitate to the island of Santorini to see its stunning caldera and the magnificent sunsets from the northern town of Oia. The island is part of the Aegean volcanic arc formed by the subduction of the African plate under the Aegean Sea. About 3,600 years ago, the island suffered a violent volcanic eruption in which much of the rocks were removed, causing the volcano to collapse and produce the caldera. About 160km northwest of Santorini and also situated on the volcanic arc is the island of Milos. The island is a more peaceful alternative to the bustling crowds of Santorini and the rich volcanic soils are renowned for producing excellent wines and vegetables. Milos is a ‘must-visit’ island for any traveller with an interest in geology visiting this area of the Greek Islands. Fig. 1. Santorini. Northward view of the eastern caldera wall and rim. There are a number of designated Geo Walks on the Milos (see How to Explore the Island below). These can be up-loaded at https://www.milosminingmuseum.com/en/the-museum/miloterranean-geo-walks/. Readers may also wish to refer to these while reading the text of this article. The geology of Milos The oldest rocks are a basement of metamorphic rocks, such as schists, gneiss and quartzites of Mesozoic to Palaeogene ages (250 to 25Ma). The basement rock is overlain by Miocene to early Pliocene (25 to 5Ma) conglomeratic and calcareous rocks. The main character of the island we see today was formed … Read More

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Book review: Geology of the Yorkshire Coast: Geologists’ Association Guide No 34 (4th edition), by Peter F Rawson and John K Wright

Jon Trevelyan (UK) This is the much anticipated 4th edition of the GA’s Yorkshire Coast guide and it was well worth the wait. From personal experience, I was aware that the previous editions were extremely good for any geologist – professional, academic or amateur – who is attracted by the wonderful scenery and fascinating geology of this part of the UK coastline. However, this new edition is altogether an even better product. The full colour photographs, diagrams and maps make for an entertaining and informative read, and a new chapter using seismic profiles provides additional information not in previous editions. Like all GA guides, this introduces the geology of the Yorkshire Coast in an accessible and readable style, including coverage of its structure, stratigraphy, palaeogeography and environments, and its industrial history. It then provides 17 excursions covering areas from Staithes in the north to South Holderness in the south. This takes in all the obvious areas that any fossil collector in the area will know – like Staithes to Port Mulgrave, Saltwick Bay to Whitby, Speeton and Flamborough Head – but also includes some new locations, such as Betton Farm Quarries, which is a SSSI. I was lucky enough to visit this fascinating site with the authors, who showed us why this excellently exposed localised, coral reef from the Upper Jurassic was worth including in the guide. (There is also an excellent charity-run tearoom and restaurant to visit after looking at the rocks.) Pete Rawson spent his academic career in … Read More

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Cresson Mine: The untold stories

Benjamin Hayden Elick and Steven Wade Veatch (USA) The Cresson mine (Fig. 1) – situated between Cripple Creek and Victor in Colorado – was established in 1894 (MacKell, 2003). No one is certain who started the mine, but records show that two brothers, insurance agents, J R and Eugene Harbeck from Chicago, were early owners. After a hard night of drinking, they sobered up the next day and learned of their new acquisition (MacKell, 2003). The Cresson Mining and Milling Company was organised a year later, in 1895, to raise capital and operate the mine (Patton and Wolf, 1915). The mine continued operating through several leases with low but steady proceeds. Fig. 1. Early view of the Cresson mine, Cripple Creek, Colorado. Photograph date, circa 1914, courtesy of the Cripple Creek District Museum. The Cresson mine became profitable when Richard Roelofs, a known mining innovator, was hired by the Harbecks as mine manager in 1895. Roelofs wrote in an undated letterhead: I was a prospector, a leaser, a miner, an assayer and chemist, an underground shift boss, foreman, superintendent and then general manager of one to the greatest of Colorado’s mines” (Roelofs, n.d.). Roelofs (Fig. 2) was a newcomer to Colorado, as many were when the Cripple Creek gold rush ignited in 1891. He moved to Cripple Creek in 1893 with his wife Mabel. They had one child, Richard Jr, who was born on 19 August 1894 in Cripple Creek. Fig. 2. Richard Roelofs, manager of the Cresson mine. Photograph date, 1914, … Read More

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Michigan Puddingstone

Steven Wade Veatch USA) Michigan’s puddingstones are intriguing rocks that look like a glob of pudding stuffed with raisins, nuts and bits of cranberries. These white rocks with small red, brown, purple and black pebbles are not a Michigan product. During the last ice age, they hitched a ride into Michigan on an ice sheet and got off in the southern part of the state when the ice melted. Puddingstones went through several steps in their formation (in what is now part of Ontario, Canada) before they went on their journey to Michigan. First, a network of rapidly flowing streams tumbled red and coffee-brown jasper, funeral-black chert, hematite and quartz in their churning water. Next, the streams deposited the material as sedimentary fill in eroded troughs and as alluvial fans when the streams reduced their velocity, and scattered the colorful pebbles onto mounds of sand (Lowey, 1985; Baumann et al, 2001). Fig. 1. An unpolished puddingstone from Michigan. Some contain trace amounts of gold and diamonds. These rocks are commonly found just after farmers plough their fields in Michigan.  Puddingstones were brought to Michigan by ice age glaciers. (Jo Beckwith specimen. Steven Veatch photograph.) Then, the sand and pebbles hardened beneath the Earth’s surface and, over time, formed sedimentary rocks known as conglomerates (Slawson, 1933). Later, intense heat and pressure metamorphosed the matrix of sand into a light-coloured, coarse-grained, sugary-textured quartzite that tightly held the pebbles (Schaetzl, n.d.). These geological forces formed the puddingstones around 2.3 billion years ago. Today, … Read More

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Flints in the Late Cretaceous Chalk of NW Europe

Rory Mortimore (UK) Flint in the Late Cretaceous Chalk: links across the European platform In a recent issue of this journal Paul Taylor wrote “We are very fortunate in Britain to host one of the most remarkable deposits in the entire geological record, the Chalk” (Deposits Issue 55, 2018, p.35, see Bryozoans in the English Chalk). Perhaps equally remarkable are the bands of flint associated with the pure white chalks (Figs. 1 to 3). Flints have attracted human attention since pre-historic times with some flint bands providing the preferred source rock for manufacturing stone-age tools (for example, the Late Turonian Floorstone Flint at Grimes Graves near Brandon in Norfolk, England (Figs. 4 to 6a and b; Mortimore and Wood, 1986), or the geologically much younger Early Campanian flints in the Harrow Hill Flint Mines in Sussex, England Fig. 7). Subsequently, Brandon flints were used as the vital spark for guns (that is, gun-flints, Skertchley, 1879; Shepherd, 1972) and these have been found as far afield as eastern North America (used in weapons of the American revolution) to the Fijian Islands in the Pacific (from Royal Navy guns). In the modern era flint remains a material of concern in engineering causing damage to core-drilling operations, tunnelling machines (Fig. 8) and cable trenching machines onshore and offshore northwest Europe. Flint also impacts the ease with which piles can be driven into chalk. To fully appreciate flint as a material and to assess the impact of flints on engineering operations has required establishing … Read More

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Guide to minerals: Aegirine

Ben Elick (USA) Aegirine is a beautiful, dark-coloured pyroxene, which is somewhat rare. It is named after Aegir, a figure in Norse mythology. The mineral has also been called acmite, derived from the Greek word “acme,” meaning point in reference to the mineral’s usually pointed crystals. The name acmite is now obsolete. The mineral was discovered in Norway and was named in 1835. Fig. 1. specimen of aegirine on a microcline matrix from, Mount Malosa, Domasi Zomba District, Malawi. This specimen is pictued with a cenitimeter scale, and measeures 4.5cm wide, 4.5cm tall and 1.5cm thick. (A Ben Elick specimen; photo by Ben Elick.) Aegirine crystals are deep green, brown or even black in colour, and typically have lengthwise striations. Crystals can have steep or blunt termination points, and the terminations are often etched and dull. They are commonly twinned. Aegirine’s clearest identifying characteristics are its distinct dark colour, crystal habit and optical properties, as aegirine can be confused with other pyroxenes. It forms a series with augite, a common pyroxene of mafic igneous rocks and commonly forms with other pyroxenes, feldspathoids, albite, sodalite and barite. Aegirine is most commonly formed in silica deficient intermediate igneous rocks, often intrusive in nature, such as nepheline syenite and syenite pegmatites. It is also found in phonolites. Although less common, it can also be found in certain types of metamorphic rocks. Notable aegirine localities include: Kongsberg, Norway; Mont Saint Hilaire, Québec, Canada; Magnet Cove, Garland County, Arkansas, USA; Kola Peninsula, Russia; Libby, Montana, … Read More

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Book review: Fossil Arachnids: Monograph Series Vol 2, by Jason A Dunlop and David Penney

This is the second of a two-part series of monographs on spiders (and arachnids more generally) involving Dr David Penney – the other is reviewed next to this. This one is written with Jason Dunlop, who has described numerous new fossil species in a variety of arachnid groups, from scorpions to harvestmen, to mites and even some extinct groups.

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Book review: Fossil Spiders: The evolutionary history of a mega-diverse order – Monograph Series Vol 1, by David Penney and Paul A Selden

This is the first of a two-part series of monographs on spiders (and arachnids more generally) involving Dr David Penney and published by Siri Scientific Press. This one is written with Dr Paul Selden, who has more than 30 years of researching, and teaching about, fossil arachnids.