Category: minerals

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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 These are often important historical documents of geology in a bygone age, no longer visible, particularly in urban environments.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.

BOOK REVIEWS fossils minerals palaeontology

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.

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World of geology

Tony Waltham (UK) This article accompanies a book review of Tony Waltham’s book, The World of Geology. The text is broadly taken from the book itself. The world of geology is the world as we know it, that we see and that we live on. It is all about the evolution of the Earth’s crust, the nearly rigid layer less than 100km thick that is the outer shell of our evolving planet. This crust is broken into a few dozen large and small tectonic plates, which move around at rates of a few centimetres a year. Originally known as continental drift when it was first recognised in 1912, this geological activity has been referred to as plate tectonics since its processes began to be properly understood during the 1960s. A large part of the Earth’s crust is the oceanic floor. The basaltic rock of the slowly moving oceanic plates is continuously being created along plate boundaries that are divergent, and destroyed along those that are convergent. These are the major processes of plate tectonics that keep Planet Earth evolving and alive. The oceanic basalts are similar to those in some types of volcano, but otherwise they remain largely unseen beneath the cold, dark and minimally explored waters of the ocean depths. The second part of the Earth’s crust is the incomplete upper layer, largely of granitic composition, that forms the continents. Along with the submerged edges known as the continental shelves, these occupy about one third of our planet’s surface. … Read More

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Geology museums of Britain: The Booth Museum of Natural History, Brighton

Jon Trevelyan (UK) Fig. 1. A group of German schoolchildren enjoy a day out at the museum. Those of you with a long memory (and an admirable loyalty to Deposits magazine) may remember that, several years ago, I produced a few articles on British geology museums, including the National Stone Centre in Derbyshire and Whitby Museum (the latter jointly with Dean Lomax). I have recently been spending some time working in the seaside town of Brighton and decided to reacquaint myself with the Booth Museum of Natural History, an to write about this quaint little gem. Fig. 2. The rows of cabinets containing the Victorian taxidermy of collector, Edward Booth. I am not entirely comfortable with the rows of cabinets full of stuffed animals containing the collection of Victorian taxidermy of collector, Edward Booth (Fig. 2) after whom the museum is named, but it is not that that attracts me to the museum. Rather, it is a smallish backroom housing a collection of geology – found predominantly in Sussex, but also elsewhere in Britain and the world. Fig. 3. A large set of gypsum crystals among other mineral exhibits at the museum. While there are iguanodontid dinosaur bones from Sussex on show, there are also large mineralogical and sedimentological specimens (and apparently petrological slides in a microscopy section, which I was not aware existed). There is also material from the elephant beds beneath Brighton, with ice age mammal fossils and subfossils. Fig. 4. Echinoids: Stereocidaris sceptrifera (left), Tylocidaris clavigera (middle) … Read More

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Excursion to the South Devon coast led by Prof John CW Cope (National Museum Wales)

Mervyn Jones (UK) GA field meeting on 6 and 7 April 2019 This field meeting was the second following the publication of Prof Cope’s GA Guide No 73, Geology of the South Devon Coast (reviewed in Issue 51 of Deposits), the companion to GA Guide No 22, Geology of the Dorset Coast (reviewed in Issue 50). Our mission for the weekend was to complete our examination of the complex Devonian succession from Torbay to the western limit of Lyme Bay at Start Point and then beyond; farther into South Devon. Of great interest was the marine Devonian, first described by Adam Sedgwick, assisted by Roderick Impey Murchison, who finally realised that these facies were contemporaneous with the familiar Old Red Sandstone found north of the Bristol Channel. The area has much to offer enthusiasts of structural geology because the Devonian strata have been tectonised by the closure of the Rheic Ocean during the Variscan orogeny. The story has only been unravelled in the last 50 years as follows. First, sediments filled a series of basins caused by crustal extension; the basement beneath the Devonian rocks may well be a massif of Precambrian mica-schist, inferred from the copious amounts of mica and the occasional xenolith in the rocks above. Then, from the Early Carboniferous, continental collision caused a series of major thrust structures and metamorphic zones that progressively moved northward. As a consequence, any Carboniferous rocks that were deposited in the Torbay area were rapidly stripped off. The marine Devonian was … Read More

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Fifteenth century magico-medicinal minerals

Chris Duffin (UK) The Hortus Sanitatis (1491) On 23 June 1491, a new volume was printed and bound for distribution in the German University town of Mainz. The publisher was Jacob von Meydenbach, who might also have been responsible for compiling many of the entries in the book. The volume was based partly on an earlier work entitled Gart der Gesundheit, which was also published in Mainz, but this time by Peter Schöffer, an apprentice of Johannes Gutenberg. This famous pioneer revolutionised mass product printing in the 1450s by developing the use of movable type. Schöffer continued to innovate in this medium after Gutenberg’s death in 1468, experimenting with page sizes, numbers of lines to a column, the arrangement of text blocks and font styles, and the use of woodcuts as illustrations. His Gart der Gesundheit, published in 1483, only a few decades after the inception of the printing revolution, was an immediate success. Meydenbach’s Hortus Sanitatis was prepared as a sort of sequel to the Gart; more ambitious in scope, it was rather longer with additional entries and, importantly for us, a section on stones (Fig. 1).Fig. 1. A double page spread from the De Lapidibus section of Hortus Sanitatis (1491). Wellcome Collection, London.Gart der Gesundheit (German) and Hortus Sanitatis (Latin) both translate as The Garden of Health, giving an indication of the thrust of the volume – here was a treatise on the medicinal virtues of materials from the natural world. The section on stones (De Lapidibus), like … Read More

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Pathway to the past: A miner’s photograph

Steven Wade Veatch (USA) Fig. 1, Robert Plews (32), with two daughters, Elizabeth (4) and Mabel (3) and his wife Janet (25), stand in front of their small home in Elkton, Colorado, one of the towns in the Cripple Creek Mining District. (Photo date circa 1899, from the S W Veatch collection.) This photograph, taken around 1899, shows my ancestors posing at their modest frame home, where they lived one step away from Cripple Creek’s gold rush world of cardplayers, whisky drinkers, and midnight carousers. The scene depicts my great-grandfather (Robert Pickering Plews), my great-grandmother (Janet Plews), and two of their daughters in front of their miner’s cabin, built from pine boards, on a hillside in the newly established mining town of Elkton, Colorado. My great-grandparents were from England. Two years after my great-grandfather married my great-grandmother, he left England – by himself – to build a better life in Cripple Creek’s goldfields for the family that he left behind. Robert Plews was a hope-chaser. He carried his dreams from England across the Atlantic and then 1,700 miles to the Front Range and Cripple Creek. He arrived in the gold mining district in 1897. Victoria was the Queen of England, William McKinley was the US President, and Marconi had sent his first wireless transmission. The Colorado Rockies meant a new chance for him at a place with unlimited opportunities. He went to work at the busy Elkton mine. After my great-grandfather established himself in the mining camp, he sent for … Read More

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Geoarchitecture of some Romanesque churches in Aquitaine, France

Nouvelle-Aquitaine (New Aquitaine) is a vast region of southwest France covering more than 30,000 square miles. Between 1154 and the end of the Hundred Years War in 1453, much of the region was under British control. Links with Britain are still strong today, both through tourism and the large ex-patriate British population, particularly in the Dordogne, known jokingly to locals as ‘Dordogneshire’.

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From pencils to programming and graphene: Graphite’s role in the transmission of knowledge

Adam Blaxhall (UK) Once a mystery substance thought to be a type of lead, graphite is now one of the most vital components in the ever-expanding world of complex electronics. But this ‘mineral of extremes’ is more than just the familiar grey material we find in pencils. Rather, it is a specific form of the element, carbon (another is diamond) and, from writing products to electrical circuitry, graphite plays an increasingly important role in how we process, communicate and transfer information – and there’s still much to learn from its untapped potential. Graphite: the only mineral for the job A popular misconception is that lead pencils are made from lead (Fig. 1). Fig. 1. Putting lead in your pencil? Graphite was originally considered to be a form of lead and went by the name ‘plumbago’. In fact, they never have been. Graphite – mistaken for a form of lead – has been the main ingredient in the pencil since the largest, purest deposit of the mineral ever discovered was unearthed in Borrowdale in Cumbria, UK in the 1500s (Fig. 2). Fig. 2. Graphite. Graphite is ideal for pencils because its giant structure of carbon atoms – formed of honeycomb-like layers stacked on top of each other – is such that the bonds between atoms are stronger than the bonds between layers. It’s this physical property that gives graphite its soft and slippy texture, and allows the layers to slide off one another. So, when a pencil moves across a surface, … Read More

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Shining hill in the Arizona desert

Deborah Painter (USA) In the area east of the small community of Bagdad and on the northeast edge of the Arrastra Mountain Wilderness of central Arizona in the USA, my friends, Terril, Yvette and David, stood with me at the base of a vision in the desert of a rockhound’s dream. This was a colourful, irregularly shaped hill, standing alone in the arid wildlands, its bright whites, reds and greens standing out against a blue and white March sky. The entire hill seemed composed entirely of loose stones of quartz, caliche (a mineral deposit of gravel, sand and nitrates found in dry areas of the USA), basalt, travertine, green quartzite, tuff and gabbro. One whole side of the hill was white from quartz. We had attempted to climb this amazing thing. But, like wonderful things in a dream, most of it eluded us. We could climb but a metre or so, before we slid back down, unable to secure a foothold. However, the four of us collected about a bucket full of the rocks on this Bureau of Land Management land. Fig. 1. Our eyes were transfixed by a shining green, brown, red and white hill (a volcanic neck), standing alone in the Central Highlands of Arizona. The side facing east (to the right in this photograph) was white from quartz. (Credits: Deborah Painter.) Just across the roadway to the south, we had hiked a short distance across an arroyo (a Spanish word for a dry creek or stream bed). … Read More

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