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Preserving geological museum collections

Dr Caroline Buttler (UK) It has long been recognised that art and archaeological collections in museums may need specialised conditions and conservation to survive. However, until relatively recently, geological collections have not had the same level of care. Perhaps, it was thought that rocks, minerals and fossils that had already survived millions of years do not need any particular attention. Although geological material may appear strong and durable, there are factors that can lead to the deterioration and even the complete destruction of specimens. The last 20 years have therefore seen a growing interest in storage conditions for geological collections with some museums appointing specialist conservators to care for them. The museum environment The museum environment is traditionally a compromise between the need to preserve objects and to provide comfortable conditions for staff and visitors. Unfortunately for specimens, when there is a conflict, human interest often wins. Environmental factors, including temperature, humidity, light and pollution, can be major threats to geological material. Temperature alone does not usually cause damage to specimens, but it can speed up the rate of deterioration and changes in temperature can affect relative humidity (RH). There are no ideal levels of temperature and relative humidity suitable for all geological material, but the commonly accepted parameters are 20oC plus or minus 2oC, and 50% plus or minus 5% RH, and air-conditioned stores are set at these. However, many specimens do not have the benefit of these conditions and, even those that do, can still degrade and fall … Read More

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Crystals and minerals of the London Clay

Bob Williams (UK) I developed a passion for crystals while collecting fossils. To me, crystals don’t have to be fancy, rare or expensive to be of immense interest. Even a good specimen of the commonly encountered “fools gold” (iron pyrite, more technically referred to as iron sulphide) will be of great interest to me. I live in south-east England, which is perhaps not the best place in the country for collecting interesting crystal specimens. However, I have a special interest in a geological deposit known as “London Clay” that is highly fossiliferous and includes fossils of crabs and lobsters. Many people will not associate this deposit with interesting minerals, but this would be to underestimate its potential. Fig. 1. London Clay, Isle of Sheppey, Kent. Crystal groups display the geometry of the crystal structure that is associated with a particular mineral and their forms can vary a great deal. The atoms, from which a substance is built, combine into structures known as “unit cells”. The atomic structure of a unit cell is then identically repeated, forming assemblies that give rise to the final crystalline form (that is, the mineral itself). Some compounds produce small, crystalline structures while others can produce individual crystals that are massive in size and striking in overall appearance. Amethyst is a good example of this and is, perhaps, the most familiar and most commercially available mineral of this type. A closer look at the crystal structure of any mineral will reveal objects of such incredible, geometric … Read More

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Scottish ‘Stones of Destiny’

Rosalind Jones (France) “Time and tide wait for no man” and “truth is often stranger than fiction.” Both these sayings apply to Scotland, especially Argyll with its islands at ‘the edge of the world’. Here, historic stones – some truly associated with destiny, others more dubiously linked by legend – fascinate and abound. Fig. 1. Perched erratic, Ben Hogh, CollColl and Tiree, to the northwest of Mull and Iona, are non-identical ‘twins’. Coll is rugged and rocky; Tiree is low, fertile and flat. However, in common with islands of the Outer Hebrides, both have pure white strands of calcareous sand made chiefly from maerl, backed by sand dunes of flower strewn machair (a low-lying grassy plain found on some of the northwest coastlines of Ireland and Scotland, in particular, the Outer Hebrides). Individually, they have their own strange, legendary stones – glacial erratics that have drawn myth to themselves and one which ‘rings’ its own warning today. Fig. 2. Sand dunes and white maerl sandy beach, Isle of Coll.Maerl is formed when Atlantic Ocean currents force upwards dissolved mineral that nourishes the marine organisms of the Hebridean fringe. From this rich cold water, calcium carbonate is extracted, not only by invertebrates to make their shells, but also by the calcareous red algae, Phymatolithon and Lithothamnion coralloides, collectively known as ‘maerl’. Found at depths of between 10m and 18m, living maerl beds produce small granules between 2mm and 10mm in size that accumulate in beds and which grow at 1mm a year. Sorted by currents and eventually washed landwards … Read More

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Mineral collecting in Slovakia

Trevor Devon (UK) Slovakia is situated at the north-western end of the Carpathian Mountains, a region well-known for its metal ore mines and quarries. One of the Sussex Mineralogical Society’s members had been a schoolteacher in Slovakia and had explored many of its mineral locations. Through his contacts there, an 11 day visit was arranged and a quite large group, comprising 17 society members, descended on the rural tranquillity of eastern Slovakia in August 2008. We were met by our two expert guides, one of whom was Dr Rudolf Ďud’a, head of the Department of Natural History in the Eastern Slovak Museum in Košice and author of the Slovakia chapter in the book Minerals of the Carpathians. Our journey took us on a round trip from eastern Slovakia up to Prešov and the Tatra Mountains on the border with Poland, across to Banská Bystrica in central Slovakia, south to šiatorská Bukovinka near the Hungarian border and back to Košice. Much of the driving was through heavily wooded mountains and attractive scenic valleys. The mines (now mostly inactive) and quarries were often well hidden, and generally required some walking (always upwards, of course) to get to from our coach. During our trip, we visited four quarries, eight mine dumps and a wooded mountainside deposit of ‘flesh opals’, so we were kept busy. One of the lasting impressions of the mine dumps (some of which were very large indeed) was the richness of secondary mineralisation – when in Cornwall, one is usually … Read More

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Gold panning at Wanlockhead, Scotland

Charlie Smart (Scotland) Today, the villages of Wanlockhead and Leadhills (the highest in Scotland) are probably best known for the centuries of toil that gave them the most productive lead mines in Scotland. However, it was the search for gold during the sixteenth century that revealed the abundance and richness of the lead veins. At the marriage of James V to Magdalene of France in 1537, cups filled with bonnet-pieces made with gold from Crawford Muir were presented as specimens of ‘Scotch fruit’. From the same district, gold was supplied to refashion an older crown for the King. This Crown of Scotland, last worn at the coronation of Charles II at Scone in 1651, is now on display in Edinburgh Castle and forms part of the ‘Honours of Scotland’. Earlier, in 1578, Sir Beavis Bulmer headed north across the Border. Having obtained letters of recommendation from Elizabeth I and, with his strong family connections to mining operations in the north of England, he was granted a patent by the Scottish Government ‘to adventure and search for gold and silver mines in the Leadhills’. Due to harsh climatic conditions, prospecting was confined to the summer months only. Nonetheless, over a period of three years, Bulmer amassed £100,000 worth of gold (in tutor values). He eventually returned to England where he presented Queen Elizabeth with a porringer (a small soup dish) made from Scottish gold. On the lintel of the house he left behind were inscribed the words, ‘In Wanlock, Elvan & … Read More

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Urban geology: Two granites

Stephen K Donovan (The Netherlands) Building stones may tell us something or nothing about the geology of the local area. As Ted Nield (2014) recently highlighted in his book, Underlands, stones used in Britain today are rarely local. Once upon a time, local stone would have been derived from a nearby quarry. Now, stones are commonly imported from overseas. If that is the case in the British Isles, then pity the poor geologist in the Netherlands, where genuine exposures of rock only occur in the south, in the province of Limburg, and mainly consist of Upper Cretaceous chalks and limestones. In consequence, ornamental and facing stones on buildings are almost invariably imported. I mainly have eyes for the imported Upper Palaeozoic limestones, probably mainly Carboniferous, but potentially including some from the Devonian. These rocks are common (van Roekel, 2007), but I also pay attention when I spy a beautiful granite, in the broadest sense, which are common on the fronts of banks and used even more extensive to clad offices. This article is about two such granites (out of many) cladding buildings in Noord Holland, which have particularly caught my eye. For a general mineralogical reference, I recommend Deer et al (1966). A faulted granite in Hoofddorp This site is close to the limestone street art in Siriusdreef (described by Donovan, 2014; and see also Fig. 1) and is an easy walk from Hoofddorp railway station or bus stops on the #300 express bus route. The building in question (there … Read More

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Rose and blue quartz

Steven Wade Veatch (USA) Quartz (SiO2) is a common mineral found in all three classes of rocks (igneous, metamorphic and sedimentary), in many environments and in a range of colours. However, rose and blue quartz are less common than some of the other varieties. This article discussed these two extraordinary minerals. Rose quartz Rose quartz has a pale pink to rose-red colour, thought to be caused by trace amounts of titanium, which absorbs all colours except pink. In a laboratory experiment, samples of rose quartz from several localities were carefully dissolved in acid. The remaining insoluble residue consisted of thin microscopic fibres, which may also be responsible for the colour of rose quartz. Well-formed rose quartz crystals are rarely found in nature, but when they are, they are generally found in massive chunks associated with pegmatites (Fig. 1). Fig. 1. This large rose quartz specimen was found at the Devil’s Hole Mine (owned by Tezaks), about a mile from the town of Cotopaxi, Colorado. (Photo © 2007 A Schaak.) The term pegmatite refers to exceptionally coarse-grained crystalline granite. Since rose quartz is cloudy, it is not popular as a faceted gem, but it is commonly made into cabochons (Fig. 2), rounded into beads for necklaces or carved into various objects. Fig, 2. A cabochon pendant from the same rose quartz near Cotopaxi. (Photo © 2007 A Schaak.) It has been named as South Dakota’s official state mineral. Here, rock hounds have a good chance of finding specimens ranging from shades … Read More

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Real ‘Southend Rock’

Bob Williams (UK) Chert and flint are crystalline (perhaps more accurately described as microcrystalline) forms of rock that man has made use of from Stone Age times. The crystals consist of a microcrystalline form of silica, more commonly known as quartz (silicon dioxide). Flint is the better-known form of this substance and is commonly found as very hard concretions in deposits of chalk. It is so hard that, when the chalk is eroded, the flint remains in an almost undamaged state. Fig. 1. The Clactonian culture ‘handaxe’ tool, which was the first tool we found at Southend beach. When fractured, flint and chert nodules disintegrate to produce conchoidal, glass-like breaks, and this creates sharp edges capable of inflicting physical damage. When controlled, this damage can be put to practical use and early species of man (Homo erectus, H habilis, H neanderthalensis and early H sapiens) recognised this fact and put it to good use in their everyday lives. During the Ice Ages, spreading ice sheets eroded many millions of flint nodules from chalk deposits and spread them all over the UK. When the ice melted during warmer interglacial periods, the nodules were deposited wherever they happened to have been transported to. Such flint nodules are referred to as “derived” nodules. Early man came to recognise them and collected them to make use of their physical properties. In this way, the first stone tools appeared and, as skill levels developed in their manufacture, they became more and more sophisticated in form. … Read More

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Moeraki Boulders: The giant marbles of New Zealand

Tasman Walker (Australia) Scattered over Koekohe Beach on the South Island of New Zealand, dozens of huge spherical boulders look like the remains of a monster game of marbles. These were recently featured on the cover of Issue 22 of Deposits. The grey, stone balls are a fascinating tourist attraction, about 70km north of Dunedin, near Moeraki, a small town on the Otago Coast. Some boulders stand alone, but most sit in clusters, with the waves splashing over them at high tide. Many lie broken into segments on the sand. Fig. 1. Large, small and broken boulders. The boulders are spectacular examples of concretions, which form when a mineral precipitates and cements the loose grains of sediment into solid rock. As you walk down the steep bluff to the beach, you can see other enormous boulders still embedded in the uncemented mudstone, but being exposed as the ocean waves erode the loose embankment. They eventually fall onto the beach. Fig. 2. Popular with tourists. The boulders come in two distinct sizes: the diameters of the smaller ones range from 46cm to 92mm, but the larger ones are 137cm to 200cm in size. The largest ones weigh almost 20 tons. Most are spherical, but a few are slightly squashed in a direction parallel to the bedding of the mudstone in which they formed. Although fascinating, the boulders are by no means unique. In New Zealand, you can find similar ones on a beach just 12km south, and others on the North … Read More

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On the origin of agate: A 300-year-old enigma

Terry Moxon (UK) Quartz has been estimated to occupy around 12% of the earth’s crust and can be found in many forms, ranging from the massive, clear crystals of quartz and amethyst to the microcrystalline quartz that is to be found in jasper, agate, chalcedony, chert and flint. World-wide, the distribution of agate is not equal, but it can be found in every continent and probably exists in every country. However, only three countries extract enough agate for world export: Botswana, Brazil and Mexico. Fig. 1. Empty gas cavities and agate amygdales in a block of Isle of Mull basalt. (Scale bar = 2cm.) Agate is most frequently found in fine-grained, igneous rocks filling gas cavities (Fig. 1), but it can also be found in sedimentary limestone hosts (Fig. 2) and fossil wood (Fig. 3). The most common agates are the wall-lining and horizontally banded types (Figs. 4 and 5 respectively). Rapid identification of agate in the field relies on the natural translucency of a fractured sample, but final confirmation is supplied by examining a thin section under a polarising microscope (Fig.6). Agate and chalcedony show a fibrous structure, whereas the quartz in flint, chert and jasper is generally granular. Granular quartz can demonstrate regular banding, but this is not agate (Fig. 7). Nevertheless, it is the colours and rhythmic banding that makes agate the most recognisable of all gemstones. Fig. 2(a) and (b) show agate in limestone from Tepee Canyon, South Dakota, USA. Note that both agates are surrounded … Read More

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Fossils in amber (Part 2): Preparation and study

Dr David Penney and Dr David Green (UK) This is the second in a series of articles concerning fossils in amber. In the first, we focused on the biodiversity of organisms in the major deposits of the world, including the techniques available for distinguishing genuine fossils from fakes (see Fossils in amber (Part 1): Biodiversity). When the first fossil amber specimens were examined back in the 1600s, only very basic microscopy was available to examine the inclusions. In recent years, great progress has been made in amber preparation procedures, photomicroscopy and advanced imaging techniques, which can all now be employed in the study of fossils in amber. Optical properties of amber To understand the rationale for the preparation techniques described below, it is worth reviewing the way light passes through amber and the way that images are formed. Amber is usually transparent or translucent. The more transparent it is, the less the light is absorbed as it travels through the specimen. As opacity increases, more light is absorbed and inclusions become more difficult to see. Arthropod inclusions are visible because they have differing opacities and refractive indices to the enclosing amber. When light rays cross boundaries between media with different refractive indices (such as amber and air) they bend. If the surface is flat and polished, the light rays bend in a predictable manner and it is easy to see what lies within. If a surface is curved, irregular, undulating or scratched, the light rays bend in different directions, depending … Read More

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Fossils in amber (Part 1): Biodiversity

Dr David Penney and Dr David Green (UK) It is almost two decades since the original blockbuster movie, Jurassic Park, brought the existence of fossil insects in amber (fossilised tree resin) into the limelight. Since then, numerous books and research papers have been published. Fossiliferous amber deposits are still being discovered, including, in recent years, the first major deposits in Africa, India and Australia. The market for fossils in amber experienced a boom in the 1990s, but it has since declined for various reasons, including fakery, copal (sub-fossil resin) being sold as genuine amber and the current economic conditions. Nevertheless, there are many reputable sources for those wishing to develop their passion for amber – a substance that has fascinated people for millennia. It has been endowed with mystical, magical and medicinal properties, and used as an artistic medium and in jewellery. However, today, it is probably most famous for the fossil insect inclusions it preserves with life-like fidelity. It is these that are the focus of this article. This is the second part of a series of articles on fossils in amber. The first is: Fossils in amber (Part 1): Preparation and study. Important fossiliferous deposits There are almost 200 known amber deposits around the world, some dating from as early as the mid-Carboniferous. Relatively few have produced abundant biological inclusions and those that do occur only in strata of Tertiary or Cretaceous age. Many of these ambers were produced by different tree families under somewhat different environmental conditions. … Read More

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Guide to minerals: Amazonite

Steven Marquez (USA) The specimen displayed is a variety of microcline feldspar, referred to as amazonite. Many jewellers love this mineral for making cabochons because of its brilliant colour, which is thought to be caused by traces of lead and water. The gemstone is called the “Stone of Hope”, because it is thought to inspire confidence and hope. The name “amazonite” comes from the Amazon River in South America. It can also be found at the Lake George area, along with smoky quartz. However, its occurrence is very limited. Fig. 1. This specimen of amazonite was mined in the Lake George area of Colorado. ASW Veatch specimen (photo Steven Marquez). Facts on fileChemical formula: KAlSi3O8Composition: potassium aluminium silicateColour: bluish green or verdigris greenCrystals: triclinicCleavage: good, two directions at 90oFracture: unevenLustre: vitreousStreak: whiteHardness: 6Transparency: noneSpecific gravity: 2.56-2.57An amazonite haiku: Microcline feldspar. Bluish or verdigris green. The perfect jewellery Further reading Chesterman, Charles W. The Audubon Society Field Guide to North American Rocks and Minerals. New York: Alfred A. Knopf, 1990. Hall, Cathy. Smithsonian Handbooks: Gemstones. New York . Dorling-Kindersley, 2002. About the author Fig. 2. Author, Steven Marquez, is active inthe study of rocks and minerals in the PikesPeak region. (Photo by Steven Veatch.) Steven Marquez is an Earth Science Scholar with the Pikes Peak Pebble Pups and is a member of the Colorado Springs Mineralogical Society. He is a frequent contributor to magazines and newspapers, and is in the 8th grade. He lives in Colorado Springs.

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Collecting minerals around the world

 Trevor Devon (UK) At some time, I suppose we have all collected rocks or minerals when we were travelling to new places, mostly as mementos, but nothing quite beats the buzz of collecting specific minerals from classic locations with like-minded colleagues. This type of collecting implies you know something of the geology and mineralogy of the location, what sort of rock to explore (often with a sledgehammer to start with) and what colour and shape the minerals are likely to be found in. Of course, it helps to travel with colleagues who have been there before and can show you what to look for. That is one of the reasons why I joined the Sussex Mineralogy and Lapidary Society (SMLS) a few years ago. Fig. 1. Behind the scenes at the mineralogy department of the Royal Ontario Museum, Toronto. Since 1980, SMLS has conducted trips to many parts of the world, including the USA and Canada, India, Namibia in Africa, and several countries in Europe. Such trips usually attract around a dozen or so participants and are often organised with a bit of tourism so that non-mineralogical spouses can join in. I have been fortunate enough to join recent SMLS trips to Cornwall, Isle of Skye, India, the South of France, the USA, Canada, the Caldbeck Fells in Cumbria, and Bulgaria. Perhaps I should start with the basic question of why I collect minerals. First of all, I think some of us are born collectors – for example, I collect … Read More

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Geological expedition along the southwest coast of Scotland

Dr Robert Sturm (Austria) Compared to the geological architecture of other European countries not exceeding a total area of 100,000km², the geology of Scotland is characterised by an unusual diversity of geological features. Due to its tectono-metamorphic complexity Scotland attracted numerous earth scientists in the eighteenth and nineteenth centuries, whose main aim was the development of theories about, on the one hand, rock formation and, on the other, metamorphic alteration of initial lithologies. Besides being the preferred target of foreign scientists, the country has also produced its own important figures in the history of geological research. In this context, James Hutton – the “father of modern geology”, after whom, for example, ‘Hutton’s Unconformity’ at Siccar Point in Berwickshire is named – has to be mentioned, but also Hugh Miller and Archibald Geikie provided valuable contributions to the enlightenment of various geological problems. Fig. 1. Geological subdivision of Scotland into four main units. Returning to the geology of Scotland, it is possible to subdivide the country into four main geological and geographical units. The Southern Uplands, which extend south of the Southern Uplands Fault, are mainly composed of sedimentary rocks dating back to the Silurian and the Devonian. The Central Lowlands or Midland Valley, which border the Southern Uplands Fault on the north, represent a rift zone that chiefly comprises Palaeozoic rocks of both sedimentary and volcanic origin. North and west of the Highland Boundary Fault lies the Highlands and Islands, which, due to their geological diversity, can be further subdivided … Read More

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Guide to minerals: Amethyst

Steven Marquez (USA) Amethyst is the violet to purple variety of quartz. It is often associated with albite and orthoclase in pegmatites. Fine specimens of amethyst can be classified as semiprecious gemstones. This specimen was found in Cripple Creek Colorado, as a near surface deposit on the David Leighton gold mine, owned by Steven Wade Veatch across from the hardware and grocery store on Teller County 1. The short, stubby amethyst crystals formed gas pockets in a hot, welded ash deposit that once covered the landscape of Cripple Creek. Amethyst is also mined in great quantities from the state of Minas Gerais in Brazil. A deep purple amethyst is commonly found in Uruguay. The colour purple is a royal colour, which is why amethyst is often used in jewellery for kings and queens. It was highly valued by Egyptians and the ancient Greeks believed that it protected against intoxication. Amethyst is the birthstone for February. Fig. 2. Note the faint crosswise striations on the surface of the amethyst crystal. This is one of the diagnostic features of quartz. The specimen is from the Steven Veatch collection. Photo by Steven Marquez. Facts on fileChemical formula: SiO2Composition: silicon dioxide; the colour is caused by iron or manganese impuritiesColour: purple, greasy lustreStreak: whiteHardness: 7Crystal system: hexagonalTransparency: transparent to translucentSpecific gravity: 2.65Lustre: vitreousCleavage: noneFracture: conchoidalTenacity: brittleGroup: silicates, tectosilicatesHaiku Brilliant purple Never ceasing to amaze Glowing like the stars About the author Fig. 2. Steven Marquez, seen working on the curation and cataloguing of the … Read More

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Book review: Introducing Mineralogy, by John Mason

I have been fortunate enough to review for this magazine a large number of books from the Dunedin series of guides introducing aspects of the different sciences, especially the earth sciences. And Introducing Mineralogy continues the high standard set by its predecessors. It is slightly larger than some of the other guides in the series, but is still beautifully illustrated, nicely written and very informative.

Book review: Guides to: The Jurassic Coast; The Lake District; and Cornwall, by Robert Westwood

These three guides by Robert Westwood are in the same simple format. All are local geological guides to specific areas of the UK and all are illustrated by lovely full colour photographs. They all contain simple, introductory geological introductions for the uninitiated, and then more detailed expositions of what makes the regions so special.

Book review: Amber: Tears of the Gods, by Neil D L Clark

Normally, I wouldn’t be interested in semi-precious stones and other pretty things. Personally, I prefer grubbing around in the dirt, perhaps for those far more beautiful, elusive and perfectly formed Cretaceous terebratulids or Silurian trilobites. However, some semi-precious stones have the advantage of also providing a tangible link to the ancient history of life.

Book review: Fossils in Amber: Remarkable snapshots of prehistoric forest life, by David Penney and David Green

Here at Deposits, we like our amber and this certainly isn’t the first book on the subject I have reviewed. In fact, over the years, we have published many articles on the fossilised sap and its inclusions, and have just finished publishing a short, two-article series by the authors of this excellent little publication.