Mysterious blue orbs of K2 granite

William Wray (USA) K2 granite is found near the base of K2, the mountain it is named after, in the Himalayas from a rarely visited site. K2, also called “Mount Goodwin Austen” is the second highest mountain in the world, rising to 8,611m (28,253 feet). K2 got its name from the British surveyor TG Montgomerie. The “K” comes from the Karakoram mountain range and the “2” means that it is the second tallest peak recorded. Fig. 1. An oval cabochon made from K2 granite found on K2, a mountain between Pakistan and China, revealing several bright blue azurite stains. The blue azurite stains formed after the granite cooled and hardened. (Photo by the author. Specimen from the William Wray collection.) K2 granite has impressive splashes of blue circles or orbs on its surface. The blue circles are azurite inside of white K2 granite rock. The white granite is fine-grained and composed of the minerals: quartz, feldspar, muscovite and biotite. The azurite stained parts of the granite, making blue dots, which range from a couple of millimetres to about two centimetres. Azurite has a relative hardness of 3.5 to 4 on the Mohs hardness scale, but assumes the hardness of the white granite, because the azurite is only a stain. The azurite formed after all the other minerals in the granite had cooled and hardened. With a hand lens or microscope, azurite spheres reveal that the azurite appears along the edges of mineral grains, in tiny fractures in the granite, and … Read More

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Colourful bluffs in Long Island recall the most recent ice age

Deborah Painter (USA) Imagine a tremendous piece of land moving equipment that scraped up the soil and some of the surface bedrock from four states within the United States’ Eastern Seaboard, carrying and dragging it all the way, before dumping it on a ridge off the shoreline. That is what essentially occurred with the final advance of the Wisconsinian ice sheet, the only one which left glacial deposits visible in New York State today. Long Island is a ridge of Cretaceous bedrock with glacial deposition. The moraines there have not been ground into sandbars and spits along the western end of the north shore as much as elsewhere, because of the sheltered nature of the Long Island Sound. Therefore, shoreline bluffs expose rocks as well as glacial loess. Fig. 1. Fishermen’s Drive takes you to the loess deposits. To park at the beach requires a permit. (Photo by JB Steadman.) If you find that your journeys take you to New York City, one of the world’s largest metropolitan areas, try to make time to visit Caumsett State Park at Long Island Sound. My own visit began when planning a visit to New York State’s Long Island to see my friend, Joyce Raber. She suggested various things that we might do: go to a Broadway play, go shopping and so forth. However, my list of things to do was typically “eco-tourist”. I wanted to visit the famed American Museum of Natural History in Manhattan, then see nearby Central Park, where the … Read More

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La Gomera: A short geological guide

Ken Madrell (UK) The island of La Gomera has an area of 370km2, it is 25km in diameter, has a maximum altitude of 1,487m (Alto Garajonay) and is situated approximately 40km west of Tenerife. Unlike the other Canary Islands, La Gomera has experienced a long and continuing eruptive break and is in a ‘postshield erosional stage’. Carracedo and Troll (2016) describe this as the stage when active volcanism has ceased, and erosive and denudational landforms are predominant (p. 39). The submarine base of the island shows that it rests on a shallower ocean bed than the surrounding islands. The emerged land mass is semi-circular in shape, with a radial drainage pattern from its centre near Alto de Garajonay. The dating of the island has proved problematic, as some of the earlier measurements placing its age between 15 Ma and 19 Ma have since proved to be inaccurate. More reliable estimates now put its age at between 10 and 11 Ma. Fig. 1. Roque Argando viewed from Lomo de la Mulata. La Gomera’s general stratigraphy comprises of three main rock sequences: (1) A Miocene basaltic shield, including a basal plutonic complex (that is igneous rock formed by solidification at considerable depth beneath the earth’s surface); (2) A nested felsic (that is, igneous rocks that are relatively rich in elements that form feldspar and quartz) stratovolcano (which is built up of alternating layers of lava and ash); and (3) The youngest Pliocene volcanism. Fig. 2. Sketch map of La Gomera, showing the … Read More

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Armboth Dyke, Lake District

Mark Wilkinson (UK) The Armboth Dyke makes a good half day geology excursion in a scenic but quiet part of the UK Lake District. Parking is on the west shore of Thirlmere, in a pay-and-display car park accessed by the narrow road that winds around that side of the lake (Grid reference NY 305 172). The car park is in an excellent setting, with direct access to the wooded lake shore, and would be a great place for the non-geologically minded to wait while you venture onto the adjacent hill. It is probably worth noting at this point that the dyke itself is mostly exposed on rather featureless rolling moorland at around 400m above sea level (Fig. 1), and might not be a good place to visit in thick mist, unless you are very confident with a map and compass. If you happen to be in the business of teaching students to make geological maps, this site makes a great practise day, without too many problems of recognising weathered rocks in the field. Fig 1. Moorland with the dyke just visible as a slightly lighter patch of rock below the red arrow, where the edge of the dyke is exposed. University of Edinburgh students for scale. So, assuming you have decent weather, leave the car park and take the path uphill from the west side of the minor road, a few metres to the north of the car park. The path is steep-ish, and can be slippery if wet, so … Read More

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Sand for arenophiles

 Dawn Walker (UK) As long as I can remember, I have collected interesting bits of rock, looking at their shapes and colours, and wondering what they were. This was fine as long as I had a garden shed of my own to keep them all in. I read some geology as a hobby and began to recognise a few of them, but then age caught up with me and I had to move to a smaller flat and there is simply no room for more rocks. In fact, I had to dispose of many of my old ones. Eventually, it dawned on me that sand is also rock, although made up of rather small pieces, and would not take up too much room, so why not collect that? After all, I was living at the seaside. Fig. 1. These translucent green grains from South Point, Hawaii, are olivine. The pounding surf erodes a forty-nine-thousandyear- old volcanic cinder cone made of olivine. As the cone erodes, the olivine crystals become beach sand. Very few beaches consist of pure olivine; however, if there is olivine in a sand, that indicates it is a volcanic region. Magnified 250 times. I really thought I had invented this hobby and was amazed to discover on the Internet that I was an arenologist or possibly an arenophile (from the Latin arena, meaning sand). There is an International Sand Collectors Society in America, which I joined, and now have email friends all over the place, with whom … Read More

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Natural wonders of the Maghreb in Morocco

Sebastian Lüning (UK) Morocco is a popular tourist destination. Most people travel to the white beaches of Agadir to sunbathe and relax, to watch the magicians on Djemaa el-Fna square in Marrakech, or to go shopping in the UNESCO-protected Osouk of Fes. However, Morocco has much more to offer. Some of the most attractive specimens found at international fossil fairs originate from this country. Morocco is home to exceptionally well-preserved trilobites and attractive Orthoceras assemblages from the Palaeozoic. The beds containing these fossils are systematically mined in the Anti-Atlas. Other fossils, such as goniatites and ammonites, complement the diverse palaeontological national treasure. Fig. 1. Location map of geological sites mentioned in this article. 1) granites near Tafraoute, 2) algal mats near Ouarzazate, 3) Ordovician glaciation, 4) Silurian graptolithic shales, 5) Orthoceras limestones, 6) Devonian mud mounds and Merzouga sand dunes, 7) Triassic Argana river sands, 8) Cascades d’Ouzoud, 9) Friouato karst shaft, 10) Dades Gorge, 11) blowholes near Agadir and Cretaceous oysters, 13) Amesfrane cliff. These fossils are part of an exciting geological past. This article aims to guide you through the highlights of Morocco’s geological history, exploring the stories behind the country’s natural wonders and its multi-million-year-old inhabitants. Concealed in its spectacular mountain chains are some fascinating snapshots from the past. Our trip will commence at the very beginning of this history and will take us gradually forward through time. We will visit various sites on a route starting in the Precambrian of the Anti-Atlas, in the southern part … 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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