Tag: calcite

england fossils geology palaeontology

Boxstones: In search of Miocene Suffolk

Tim Holt-Wilson (UK) The date is 24 May 2014 and I am browsing across East Lane Beach at Bawdsey in southeast Suffolk. A brown lump of sandstone with a white fossil shell impression catches my eye. A boxstone. This is the first one I have ever found with a fossil in it. Looking closely, I see that the sea has abraded the shell’s outlines, although the margins have survived better than the rest, so it should be possible to identify the specimen (Fig. 1). Fig. 1. Boxstone, found 24 May 2014. Boxstones are fragments of a vanished world. They are all that remains of a lost geological stratum in Suffolk called the ‘Trimley Sands’ (Balson, 1990), although deposits of similar age are still present across the sea in Belgium and other parts of Europe. Boxstones are lumps or concretions of brown sandstone, which may contain shell fossils and – if you are extremely lucky – bones and teeth. They are beach-rolled and rounded, and typically measure between 5 and 15cm in diameter. The sand is mostly quartzose, with a rich assemblage of secondary minerals, and is cemented with carbonate-fluorapatite (a phosphate mineral) and calcite (Mathers and Smith, 2002). Boxstones can be found scattered sparsely across the shingle beaches at Bawdsey and Felixstowe Ferry (Fig. 2), and in situ as a common component of the basement beds (nodule beds) at the base of the Coralline Crag and Red Crag formations of southeast Suffolk (Fig. 3). They are eroding out of the … Read More

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geology minerals north america volcanoes

Volancoes of Big Island, Hawaii (Part 1)

Dr Trevor Watts (UK) We (my wife Chris and I) enjoyed our fourth visit to Big Island Hawaii in May 2013 so much that we decided to return to the same places in October 2014. We were hoping to see similar events and activities, which we had found particularly interesting and accessible over the years. Every time we visit, something changes or isn’t possible, but this time was a little more changeable than most. The intervention of three ladies altered a few of our plans – Iselle, the hurricane that visited the southeast of Big Island two months before we arrived; Madame Pele, the Hawaiian Goddess of the Volcano; and Ana, the hurricane that hit the area during our stay. The three interventions illustrate the simple fact that we and our little plans have to be adaptable and show that some of the great locations will be discussed in these articles and will be missed if you only make one visit. This is the first of three articles on Big Island in Hawaii. In them, I will talk about the major highlights of our visit in connection with the volcanic activity of this wonderful island. This first part will mostly illustrate the different volcanic concepts that need to be understood to appreciate what can be seen, and will also provide a general background to the location and the significant summer 2014 flow towards Pahoa. About lava Traditionally, lava is described as pahoehoe or a’a. These are taken to mean ropey … Read More

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europe historical / biographies minerals mining museums, societies urban, art, anthropology

Marble from the Isle of Paros in Ancient Greece: A tour of the ancient quarries

Dr Robert Sturm (Austria) This is the second of four articles on the quarries of the ancient world and later, and, in particular, the marble that was quarried there and the artwork that was made from it. The first was Mining in Ancient Greece and Rome. Some introductory words In general, marble represents a coarse-grained metamorphic rock primarily consisting of the minerals calcite (CaCO3) and dolomite ((Ca,Mg) (CO3)2). The word ‘marble’ may be derived from the Greek term ‘marmaros’ (μάρμαρος), which means ‘shiny stone’. The earliest use of the rock dates back to the fourth millenium BC, when it was considered, for the first time, as appropriate material for the construction of buildings and the production of rather primitive sculptures. In the Classical era starting at the beginning of the fifth century BC, its use was subject to a remarkable increase, which, among other things, entailed the prevailance of this shiny material in ancient Greek architecture and sculptural art. At that time, marble was simply termed ‘white stone’ or ‘Pentelic, Hymettus or Parian stone’, thereby indicating its preferential origin from the quarries of Naxos, Paros and Mount Pentelicus. Although these mines attained extraordinary eminence in antiquity, marble was also exploited from the quarries of Eleusis, Tripoli, Argos, Selinus, Syracuse, Skyros and other places. Marble from Paros – a very particular stone Each marble originating from a local quarry is characterised by very specific features. Stone material from Mount Pentelicus is distinguished by its white colour and fine-grained texture, rather high … Read More

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minerals

Agate: A mineral that develops with age, water and moganite

Terry Moxon (UK) Agate is banded or variegated chalcedony and this distinctive appearance allows a ready identification from any source. Many agate thick sections from basic igneous hosts are reminiscent of a series of distorted onion-like rings with the initial bands closely replicating the shape of the supporting gas cavity. However, the banding is frequently distorted and this general pattern is known under various names, for example, fortification or wall lining. A second type is less common and demonstrates apparently gravity-controlled horizontal bands. Agate host rocks are varied but the most abundant agate sources are the gas cavities of basic igneous rocks. This article limits discussion to agates from these basic hosts. However, agates can also be found in some igneous acidic hosts (for example, rhyolite), sedimentary rocks (for example, limestone) and in some fossils. Agate is greater than 97% silica (SiO2) and shows little variation between different samples. Under normal earth surface conditions, silica occurs in a number of forms. It is most commonly found as alpha-quartz and this is the major component in agate. A second silica constituent is moganite with a concentration at 2 to 25%. Moganite is found in agate that has not been heated by metamorphism or in the laboratory. Together with alpha-quartz, they are usually the only forms of silica identified in agate. However, other forms of silica such as cristobalite and tridymite have been occasionally identified in agate. In agates from basic igneous hosts, calcite is a rarity, as demonstrated by an examination … Read More

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minerals wales

Mineral classics from Wales

Tom Cotterell (UK) Ask any mineral collector to name a classic mineral locality or region in Britain and they will probably think of Cornwall or Devon, perhaps Weardale in Co Durham, or even the Caldbeck Fells or the West Cumbrian iron mining district in Cumbria – but probably not Wales. This is not to say that Wales has no classic minerals, but is perhaps a reflection of collecting habits and the preference for large, brightly coloured crystals. Wales has a long history of mining dating back to, at least, the Bronze Age, but, unlike some other regions, there does not appear to have been a desire by miners to extract mineral specimens for sale. Indeed, a network of mineral dealers, as was clearly present in Cornwall during the nineteenth and twentieth centuries, was totally absent in Wales. One factor is that the establishment of a National Museum in Wales occurred relatively late (in 1907) and did not open to the general public until the 1920s. Before this, there was no central repository for specimens collected in Wales and, consequently, mineral collections with historical significance are rare in the Principality. The university colleges founded during the 1870s and 1880s built up their own academic collections. Earlier still, the Royal Institute of South Wales (founded in Swansea in 1835), established geological collections, but its focus appears (from what records remain) to have been wide ranging and not specific to Wales. Therefore, during the heyday of mining in Wales, the lack of one … Read More

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minerals

Collecting fluorescent minerals

Clay Carkin (USA) Compared to the collection of fossils and traditional mineral specimens, the hobby of collecting fluorescent minerals is in its infancy. Even though Sir George Stokes discovered the property of fluorescence in the early 1800s (from the blue glow of fluorite in sunlight), it was not until the 1940s that portable ultraviolet (UV) lamps became available to the public. During WWII, the United States needed the metal tungsten, which is present in the mineral scheelite. Mr Thomas S Warren (president and founder of Ultra-Violet Products Inc.) invented a portable ultraviolet lamp to help prospectors locate deposits of this strategic metal. In doing so, not only did Mr Warren advance the commercial application of UV lights, he also made the lamps available to hobbyists. Fig. 1. Left to right: Danielle Morency, Patricia Lyons, Leanna Smith, Audrey Balzer, Clay Carkin. This is my fluorescent mineral display team. Today, there are around eight manufacturers of ultraviolet lamps. The lamps come in all shapes and sizes, but all have a source of either short wave, mid wave or long wave UV light. You can purchase an AC lamp for home use, or a DC lamp with a 12 volt battery pack to take into the field. Collecting fluorescent minerals in daylight hours is possible, but a tarpaulin or gas grill cover is necessary if you are going to try. However, the real thrill is in night collecting, where the full effect of the UV rays can be observed without the brilliance of … Read More

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geology minerals

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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