February 2016

Major Jurassic Fossil Site Found in Argentina

0 Earth History, extinction, Fossils 3:47 PM

Major Jurassic Fossil Site Found in Argentina

The fossils were preserved almost immediately, in less than a day in some cases. (Representational Image) Paleontologists in Argenti...

Did you know? 10 Facts about San Andreas Fault

3 earth, edu, Geology, Tectonic, USA 3:41 PM

Did you know? 10 Facts about San Andreas Fault

Aerial photo of the San Andreas Fault in the Carrizo Plain The San Andreas Fault is a continental transform fault that extends rough...

Super-Rare Minerals Make Earth Unique in Cosmos

0 Geology, Mineralogy, moon, NASA 3:00 PM

Super-Rare Minerals Make Earth Unique in Cosmos

One of the Earth’s rarest minerals is Nevadaite, which has only been found in two places on the planet. These Rare Minerals Make The...

How to make a tiny volcanic island

0 earth, Geology, volcano 2:45 PM

How to make a tiny volcanic island

Niijima island spews jets of steam and ash near Nishinoshima island on November 2013. Niijima On Nov. 20, 2013, the Japan Maritime...

Giant Freezing Waves Infused with Ice Slowly Roll in off the Coast of Nantucket

0 earth 2:41 PM

Giant Freezing Waves Infused with Ice Slowly Roll in off the Coast of Nantucket

Photo © Jonathan Nimerfroh Photographer Jonathan Nimerfroh spotted ocean waves frozen over with slush off the Nantucket coast amid belo...

Soil mapping may indicate success of brush control method

0 earth, Geology, soil 1:47 PM

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<i><span data-offset-key="1olm-0-0"><span data-text="true">Mapping the long-term reaction of woody plants to brush-control techniques can help landowners prioritize management practices to maximize the effectiveness of costly brush reduction, according to a Texas A&M AgriLife Research study.</span></span></i></div>
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<span data-offset-key="7hd71-0-0"><span data-text="true">Determining how soil texture impacts the resilience of a shrubland can help achieve the best use of funds for increasing the effectiveness and duration of brush removal, said Dr. Bill Rogers, AgriLife Research professor in College Station.</span></span></div>
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<span data-offset-key="et2gd-0-0"><span data-text="true">"Shrubland resilience varies across soil types: implications for operationalizing resilience in ecological restoration," is the title of the study published in the journal Ecological Applications.</span></span></div>
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<span data-offset-key="9rgfj-0-0"><span data-text="true">The paper is authored by Dr. Carissa Wonkka and Dr. Dirac Twidwell, both former graduate students of Rogers now at the University of Nebraska-Lincoln, and Dr. Jason West and Rogers, both in the Texas A&M University department of ecosystem science and management.</span></span></div>
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<span data-offset-key="5du8o-0-0"><span data-text="true">Rogers said scientists and land managers have been trying to use scientific principles for brush control, "but it's all been kind of arm-wavy with terms such as thresholds, transitions and alternative steady states being discussed but with limited success applying them to real-world problems."</span></span></div>
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<span data-offset-key="4r6ff-0-0"><span data-text="true">The difficult reality is land managers need to be able to identify when a threshold, which is the transition between two different vegetative states, is about to be crossed and also figure out how to intervene using various management efforts to return the ecosystem to the more desired state, he said.</span></span></div>
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<span data-offset-key="a4o42-0-0"><span data-text="true">For instance, Rogers said, if grassland existed for many years until junipers began encroaching and turning the site to shrubland, this change becomes exceptionally difficult to restore to grassland and can affect the value and use of that property.</span></span></div>
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<span data-offset-key="fgo9n-0-0"><span data-text="true">"We haven't quantified these thresholds yet to be able to say what is required to effectively restore encroached rangelands," Rogers said. "We want to take these ideas and find a way to make them more useful, but it's really hard to do."</span></span></div>
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<span data-offset-key="bltnc-0-0"><span data-text="true">The study approached the situation from a more operational standpoint and looked at using traditional brush management techniques, but assessing their effectiveness across different soil types, he said.</span></span></div>
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<span data-offset-key="7l6lj-0-0"><span data-text="true">"By looking at the trajectory of the plant community following brush management techniques across different soil types, we were able to identify the resilience of shrub communities on certain soils to those management efforts," Wonkka said.</span></span></div>
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<span data-offset-key="3jqfe-0-0"><span data-text="true">Knowing the resilience of shrub communities on different soils will allow land managers to determine where to invest time and money on brush management in order to get the most out of their expenditure, Rogers said.</span></span></div>
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<span data-offset-key="c2hcn-0-0"><span data-text="true">The study was funded by the Wintergarden Groundwater District, with West as the principal investigator. West was studying how different brush management strategies influenced groundwater recharge of the Carrizo-Wilcox Aquifer.</span></span></div>
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<span data-offset-key="51fv9-0-0"><span data-text="true">"We were able to set up on a private ranch and look at how different treatments affected not only groundwater recharge, but also the plant community dynamics and how they responded to the various management practices," Rogers said.</span></span></div>
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<span data-offset-key="eneu0-0-0"><span data-text="true">Brush removal is more effective at restoring grasslands in shrub communities on fine-textured clay soils than on coarse-textured sandy soils, which are more resistant to brush removal techniques, Wonkka said.</span></span></div>
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<span data-offset-key="43sr5-0-0"><span data-text="true">"Shrubland resilience to chemical and mechanical brush removal was highest on coarse soils," she said. "On these soils, brush removal temporarily restored grassland dominance, but woody plants quickly regained pretreatment levels.</span></span></div>
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<span data-offset-key="pkkn-0-0"><span data-text="true">"However, shrublands on fine soils did not recover following treatments, continuing to be grass-dominated for the duration of the study."</span></span></div>
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<span data-offset-key="e0qg4-0-0"><span data-text="true">Wonkka said this study highlights a simple approach for prioritizing restoration actions by mapping the locations of different soil attributes that support shrub-dominated areas with differing levels of resilience to brush control.</span></span></div>
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<span data-offset-key="9m04e-0-0"><span data-text="true">"We believe this study will provide scientific insights that will translate into management improvements that will help rangeland restoration and eventually food production," Rogers said.</span></span></div>
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<span data-offset-key="f0ll8-0-0"></span><br data-text="true" /><u><i><span style="font-size: x-small;"><span style="font-family: inherit;"><span style="background-color: white; color: #333333; display: inline ! important; float: none; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 18.1818px; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;">The above post is reprinted from<span class="Apple-converted-space"> </span></span><a href="http://today.agrilife.org/2016/02/13/soil-mapping-may-indicate-success-of-brush-control-method/" rel="nofollow" style="background-color: white; border-radius: 0px ! important; box-sizing: border-box; color: #4c7a9f; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 18.1818px; text-align: start; text-decoration: none; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" target="_blank">materials</a><span style="background-color: white; color: #333333; display: inline ! important; float: none; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 18.1818px; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="Apple-converted-space"> </span>provided by<span class="Apple-converted-space"> </span></span><a href="http://today.agrilife.org/" rel="nofollow" style="background-color: white; border-radius: 0px ! important; box-sizing: border-box; color: #4c7a9f; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 18.1818px; text-align: start; text-decoration: none; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" target="_blank"><strong style="border-radius: 0px ! important; box-sizing: border-box; font-weight: bold;">Texas A&M AgriLife Communications</strong></a><span style="background-color: white; color: #333333; display: inline ! important; float: none; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 18.1818px; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;">.</span></span></span></i></u></div>
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Soil mapping may indicate success of brush control method

Soil Classification Map Mapping the long-term reaction of woody plants to brush-control techniques can help landowners prior...

World's large river deltas continue to degrade from human activity

0 delta, environmental, Geology 2:06 PM

World's large river deltas continue to degrade from human activity

Mississippi River Delta From the Yellow River in China to the Mississippi River in Louisiana, researchers are racing to better u...

A New Way to Understand the World's Rarest Minerals

0 gemstones, Geology, Mineralogy 1:50 PM

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<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-Kf_ABseRw7w/V6IPqzLCVyI/AAAAAAAAJRs/oG7xMLXLlSIbabELRjQMPD4nsTWOo-sXACLcB/s1600/A%2BNew%2BWay%2Bto%2BUnderstand%2Bthe%2BWorld%2527s%2BRarest%2BMinerals.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="334" src="https://4.bp.blogspot.com/-Kf_ABseRw7w/V6IPqzLCVyI/AAAAAAAAJRs/oG7xMLXLlSIbabELRjQMPD4nsTWOo-sXACLcB/s640/A%2BNew%2BWay%2Bto%2BUnderstand%2Bthe%2BWorld%2527s%2BRarest%2BMinerals.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Ceylon Sapphires, Tanzanian Spinel, Nigerian Spessartite, Pakistani Peridot and Paraiba Tourmaline from Mozambique. Copyright ©Thai Lanka Trading Ltd</td></tr>
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<i>Two geologists have developed a system for classifying some of the most elusive substances on the planet.</i><br />
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Of the more than 5,000 minerals recognized by geologists, fewer than 100 are thought to constitute 99 percent of the Earth’s crust. Much more than that—over half of all known minerals, in fact—are considered rare, meaning they appear in five or fewer locations on Earth.<br />
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And then there are the rarest of the rare: the minerals that have a total known volume of less than one cubic centimeter, or smaller than the size of a sugar cube. Those are the ones that Robert Hazen, a researcher at the Carnegie Institution, and Jesse Ausubel, an environmental scientist at Rockefeller University, like to study.<br />
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“Many of those minerals are known from a single microscopic find, sometimes only one crystal,” Hanzen wrote in an email. “And in some cases those crystals wash away when it rains. So those are really rare minerals!”<br />
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Minerals include gemstones, like diamonds (a form of carbon) and rubies (a form of corundum tainted with chromium), as well as more mundane things, like calcite (chalk) and halite (salt). Any naturally occurring substance of a defined chemical composition that can form into a crystal is considered a mineral. (Ordinary rocks are not minerals in and of themselves, but some are a mishmash of several different minerals.)<br />
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In a forthcoming paper in the journal American Minerologist, Hazen and Ausubel outlined a new mineral-classification system to help geologists better understand the designation of “rare.” They based their work on a similar system by the biologist Deborah Rabinowitz, who studied rare biological species. According to Rabinowitz, a species can be considered rare if it meets at least one of three criteria: a small geographic range, highly specific habitat requirements, or a small population size.<br />
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Hazen and Ausbuel similarly argue that in a rare mineral must meet at least one of four criteria. The first is a narrow range of stability, meaning that it’s found only in very specific conditions.  The mineral hazenite, for instance, can only form on the decomposed remains of cyanobacteria in super-salty, highly alkaline environments. Mono Lake, California, is currently the only known source of hazenite.<br />
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The second criterion is a composition that includes rare elements, or elements that rarely occur together in nature. Senaite, with the chemical formula Pb(Mn,Y, U)(Fe,Zn)2(Ti,Fe,Cr,V)18(O,OH)38, requires 11 different chemical elements—lead, manganese, yttrium, uranium, iron, zinc, titanium, chromium, vanadium, oxygen, and hydrogen—organized in a highly precise manner.<br />
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The third is a mineral’s transience in ambient conditions. Plenty of minerals are unable to withstand extreme environments, but some can be destroyed by pressures and temperatures that humans find tolerable. One such mineral is methane hydrate (a.k.a. methane clathrate), which can form in cold, high-pressure environments like the ocean floor. A potentially important source of energy or greenhouse gas, methane hydrate evaporates when it is brought to the surface. And researchers have identified a few vampire-like minerals, like the mercury-containing edoylerite, that are destroyed by sunlight.<br />
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The fourth and final criterion is sampling bias, meaning a mineral may be considered rare simply because scientists have a hard time finding it. Minerals that can only be seen with a microscope or are beyond geologists’ reach–such as those deep in Earth’s crust or mantle–will logically seem rare, even if they may actually be quite common.<br />
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Understanding rare minerals can also help scientists identify new ones. But more intriguingly, the study of rare minerals may shed some light on the origins of life. Hazen and Ausubel argue in their paper that Earth appears to be more mineralogically diverse than the other planets and moons in the solar system, meaning that rare minerals may have played a role in helping the earliest life forms to emerge. On the flip side, some rare minerals only form due to biological activity. Either way, the two scientists believe, the presence of rare minerals on other planets—ones we’ve seen here on Earth in tiny doses, or ones we’ve never even encountered—could possibly be a sign of extraterrestrial life.<br />
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<u><i>The original article was written by Alex Berezow  </i></u></div>

A New Way to Understand the World's Rarest Minerals

Plastic Has Become Part Of Earth's Geology

0 earth, environmental, Geology 12:59 PM

Plastic Has Become Part Of Earth's Geology

Representative photo Humans have made enough plastic since the second world war to coat the Earth entirely in clingfilm, an internation...

How does Earth's continental crust form?

0 earth, Geology, Tectonic 2:07 PM

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<tr><td class="tr-caption" style="text-align: center;"><span style="background-color: #f1f1f1; color: #888888; display: inline; float: none; font-family: "arial" , sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 16px; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;">As the hot peridotite rises, the drop in pressure causes the rock to melt (starts at 30-40 km depth). As small bits of peridotite melts, it forms basalt.</span></td></tr>
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<div class="" data-block="true" data-offset-key="8m5rt-0-0"><div class="_1mf _1mj" data-offset-key="8m5rt-0-0"><i><span data-offset-key="8m5rt-0-0"><span data-text="true">Deep beneath Alaska's Aleutian Islands, down where the pressure and temperatures have become so high that rock starts to flow, new continental crust is being born.</span></span></i></div></div><div class="" data-block="true" data-offset-key="am8e-0-0"><div class="_1mf _1mj" data-offset-key="am8e-0-0"><span data-offset-key="am8e-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="9m02p-0-0"><div class="_1mf _1mj" data-offset-key="9m02p-0-0"><span data-offset-key="9m02p-0-0"><span data-text="true">Scientists have long believed that continental crust forms in volcanic arcs – they know the magma brought up in the arcs' volcanoes is geochemically very similar to continental crust. The lingering question has been how exactly that happens. While the magma that reaches the surface is similar to continental crust, the lower crust beneath volcanic arcs is quite different from the lower half of continental crust.</span></span></div></div><div class="" data-block="true" data-offset-key="atsqk-0-0"><div class="_1mf _1mj" data-offset-key="atsqk-0-0"><span data-offset-key="atsqk-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="algp2-0-0"><div class="_1mf _1mj" data-offset-key="algp2-0-0"><span data-offset-key="algp2-0-0"><span data-text="true">A new study appearing in this week's Nature Geoscience raises questions about one popular theory and provides new support for another, in which arc lava from the surface and shallow "plutons" – magma that solidified without erupting – are pulled down into the Earth at subduction zones and then rise up to accumulate at the bottom of the arc crust like steam on a kitchen ceiling. Scientists have found compelling evidence to suggest that this could have produced the vast majority of lower continental crust through Earth history.</span></span></div></div><div class="" data-block="true" data-offset-key="4nhno-0-0"><div class="_1mf _1mj" data-offset-key="4nhno-0-0"><span data-offset-key="4nhno-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="9ckqp-0-0"><div class="_1mf _1mj" data-offset-key="9ckqp-0-0"><span data-offset-key="9ckqp-0-0"><span data-text="true">The process, called relamination, starts at the edge of a continental plate, where an oceanic plate is diving under the continental plate and magma is rising to form a volcanic arc. As the oceanic plate dives, it drags down sediment, lava and plutonic rock from the edge of the arc. As arc material descends, minerals within it become unstable with the rising pressure and heat, and they undergo chemical changes. New minerals form, and chunks of the rock and sediment can break off. When those chunks are denser than the mantle rock around them, they continue to sink. But when they are less dense, such as those that form silica-rich granulites, they become buoyant and float upward until they reach the bottom of the arc crust and accumulate there.</span></span></div></div><div class="" data-block="true" data-offset-key="caibj-0-0"><div class="_1mf _1mj" data-offset-key="caibj-0-0"><span data-offset-key="caibj-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="d39rl-0-0"><div class="_1mf _1mj" data-offset-key="d39rl-0-0"><span data-offset-key="d39rl-0-0"><span data-text="true">"Sediments are really well represented in continental lower crust, but how did they get on to the bottom of the continent? The easiest way is for that sediment to be pushed down a subduction zone and rise to accumulate at the base of the crust," said Peter Kelemen, a geochemist at Columbia University's Lamont-Doherty Earth Observatory and author of the paper with Mark Behn of Woods Hole Oceanographic Institution.</span></span></div><div class="_1mf _1mj" data-offset-key="d39rl-0-0"></div></div><div class="" data-block="true" data-offset-key="8047i-0-0"><div class="_1mf _1mj" data-offset-key="8047i-0-0"><span data-offset-key="8047i-0-0"><span data-text="true"> </span></span></div></div><div class="" data-block="true" data-offset-key="dijdn-0-0"><div class="_1mf _1mj" data-offset-key="dijdn-0-0"><b><span data-offset-key="dijdn-0-0"><span data-text="true">Sampling the Earth's Crust</span></span></b></div></div><div class="" data-block="true" data-offset-key="f1ve8-0-0"><div class="_1mf _1mj" data-offset-key="f1ve8-0-0"><span data-offset-key="f1ve8-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="fs22b-0-0"><div class="_1mf _1mj" data-offset-key="fs22b-0-0"><span data-offset-key="fs22b-0-0"><span data-text="true">To determine how arc crust could turn into continental crust, Kelemen and Behn examined the only two known sites where a complete section of arc lower crust is visible on land. One site, in Pakistan, had been caught in the ancient collision of tectonic plates between India and Asia, and was thrust up into steep mountains. The other, the Talkeetna arc stretching from the Alaska Peninsula to Valdez, was pushed up at the edge of North America.</span></span></div></div><div class="" data-block="true" data-offset-key="bshac-0-0"><div class="_1mf _1mj" data-offset-key="bshac-0-0"><div style="width:100%;margin: 0px auto"><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script><br />
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</div><span data-offset-key="bshac-0-0"><span data-text="true">"We don't usually get to see the bottoms of arc lower crust, but in Alaska and Pakistan we can see right down to the bottom. These old arcs formed, crashed into North America, turned on their sides, and were eroded over millions of years. Because they're tilted, we can walk right down from the seafloor, past the base of the crust and into the mantle," Kelemen said.</span></span></div></div><div class="" data-block="true" data-offset-key="14d98-0-0"><div class="_1mf _1mj" data-offset-key="14d98-0-0"><span data-offset-key="14d98-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="60fk0-0-0"><div class="_1mf _1mj" data-offset-key="60fk0-0-0"><span data-offset-key="60fk0-0-0"><span data-text="true">Along the length of these areas of exposed arc crust, the scientists took samples to see how the geochemical composition of the rock changed with increasing depth in the crust. They were able to extract minerals that had recorded the pressure and temperature at the point where the minerals crystalized deep underground, marking how deep the rock was at each point.</span></span></div></div><div class="" data-block="true" data-offset-key="9cntp-0-0"><div class="_1mf _1mj" data-offset-key="9cntp-0-0"><span data-offset-key="9cntp-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="6el38-0-0"><div class="_1mf _1mj" data-offset-key="6el38-0-0"><span data-offset-key="6el38-0-0"><span data-text="true">The scientists found significant changes in the crustal composition about half way down into the arc crust.</span></span></div></div><div class="" data-block="true" data-offset-key="4qeqg-0-0"><div class="_1mf _1mj" data-offset-key="4qeqg-0-0"><span data-offset-key="4qeqg-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="4e00o-0-0"><div class="_1mf _1mj" data-offset-key="4e00o-0-0"><span data-offset-key="4e00o-0-0"><span data-text="true">In the lower half of the arc crust, starting about 20 kilometers below the original surface, the average concentration of "incompatible" trace elements – elements like tantalum and potassium that prefer to remain in melt during crystallization – was much less than in lower continental crust at the same depth. It was only the upper 20 kilometers of the arc crust that had compositions similar to lower continental crust.</span></span></div></div><div class="" data-block="true" data-offset-key="a7hul-0-0"><div class="_1mf _1mj" data-offset-key="a7hul-0-0"><span data-offset-key="a7hul-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="a7ivu-0-0"><div class="_1mf _1mj" data-offset-key="a7ivu-0-0"><span data-offset-key="a7ivu-0-0"><span data-text="true">That becomes a problem for one leading theory of how continental crust forms, Kelemen said. That theory suggests that the arc crust delaminates – dense bits of rock within the arc crust slowly move downward and "founder" into the mantle until the arc crust attains the composition of continental crust. The new data suggests that for delamination to work would require removing much of the rock from a 20-kilometer thickness of crust. However, delamination only works below 35 to 40 km depth.</span></span></div></div><div class="" data-block="true" data-offset-key="f4ve4-0-0"><div class="_1mf _1mj" data-offset-key="f4ve4-0-0"><span data-offset-key="f4ve4-0-0"><span data-text="true">"So, even after we remove a bit of dense stuff off the bottom, you're still going to end up with lower crust in the arcs that looks really different from lower crust in the continents. The process isn't sufficient to make continental lower crust out of arc crust," Kelemen said. Delamination does take place, but for it to be the driving force would require a complex process of repeated crustal thickening and metamorphic events, he said.</span></span></div></div><div class="" data-block="true" data-offset-key="1e50b-0-0"><div class="_1mf _1mj" data-offset-key="1e50b-0-0"><span data-offset-key="1e50b-0-0"><span data-text="true">Kelemen and Behn suggest a simpler process.</span></span></div></div><div class="" data-block="true" data-offset-key="76ikc-0-0"><div class="_1mf _1mj" data-offset-key="76ikc-0-0"><span data-offset-key="76ikc-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="e2k3b-0-0"><div class="_1mf _1mj" data-offset-key="e2k3b-0-0"><b><span data-offset-key="e2k3b-0-0"><span data-text="true">The Aleutian Islands Test</span></span></b></div></div><div class="" data-block="true" data-offset-key="aatfu-0-0"><div class="_1mf _1mj" data-offset-key="aatfu-0-0"><span data-offset-key="aatfu-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="1lntd-0-0"><div class="_1mf _1mj" data-offset-key="1lntd-0-0"><span data-offset-key="1lntd-0-0"><span data-text="true">The authors put their model to the test on the Aleutian Islands. In that volcanic arc, the lava and plutons are similar to continental crust, but the lower crust is highly depleted in elements that are abundant in lower continental crust. To determine the potential for relamination to produce lower continental crust, the scientists calculated the density of the exposed lava and plutons at subduction zone pressures and temperatures.</span></span></div></div><div class="" data-block="true" data-offset-key="5qfd7-0-0"><div class="_1mf _1mj" data-offset-key="5qfd7-0-0"><span data-offset-key="5qfd7-0-0"><span data-text="true">About 44 percent of the Aleutian lavas and 78 percent of the plutons would be more buoyant than mantle peridotite under subduction zone conditions, they found. This suggests that if parts of the Aleutian arc are pulled down into the subduction zone, at a depth of 90 to 120 km, where temperatures exceed 700°C, the arc lavas and plutons would rise to accumulate along the bottom of the crust. The composition of this accumulated material would look like lower continental crust.</span></span></div></div><div class="" data-block="true" data-offset-key="k2ti-0-0"><div class="_1mf _1mj" data-offset-key="k2ti-0-0"><span data-offset-key="k2ti-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="8bsui-0-0"><div class="_1mf _1mj" data-offset-key="8bsui-0-0"><span data-offset-key="8bsui-0-0"><span data-text="true">Intrigued by that finding, the scientists performed the same calculations for other arcs. They found that at the Alaska Talkeetna site, 48 percent of lavas and 37 percent of plutons would be buoyant. At Kohistan, the site in Pakistan, 36 percent of lavas and 29 percent of plutons would be buoyant.</span></span></div></div><div class="" data-block="true" data-offset-key="1u28p-0-0"><div class="_1mf _1mj" data-offset-key="1u28p-0-0"><span data-offset-key="1u28p-0-0"><span data-text="true">Relamination may be evident in Southern California's Pelona Schist where sections of lower continental crust are visible, Kelemen said. Clay rocks and blobs of mantle peridotite surrounded by more buoyant materials can be found in the exposed, "underplated" crust.</span></span></div></div><div class="" data-block="true" data-offset-key="5i0o6-0-0"><div class="_1mf _1mj" data-offset-key="5i0o6-0-0"><span data-offset-key="5i0o6-0-0"><br data-text="true" /></span></div></div><div class="" data-block="true" data-offset-key="bvose-0-0"><div class="_1mf _1mj" data-offset-key="bvose-0-0"><span data-offset-key="bvose-0-0"><span data-text="true">"We can see young, volcanic sediments that were stuffed under older continental crust and are now part of the overall package. How did they get down there? It happened in Southern California, and I would argue it probably happens in a lot of places," Kelemen said.</span></span></div></div><div class="" data-block="true" data-offset-key="376hv-0-0"><div class="_1mf _1mj" data-offset-key="376hv-0-0"><br data-text="true" /> <a href="http://dx.doi.org/10.1038/ngeo2662" rel="nofollow" target="_blank"><span data-offset-key="c1vbc-0-0"><span data-text="true">Journal reference: Nature Geoscience</span></span></a></div><div class="_1mf _1mj" data-offset-key="376hv-0-0"><u><span data-offset-key="c1vbc-0-0"><span data-text="true"> Provided by: Columbia University</span></span></u></div></div></div>

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10 Interesting Facts About Geodes

0 earth, Geochemistry, Geology, Mineralogy, minning 1:55 PM

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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-JhKvzDyvrtw/VsrlNFg87jI/AAAAAAAAH30/P3xO2CDputg/s1600/Thunder%2Begg%2Bis%2Ba%2Bnodule-like%2Brock%2B-geology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="327" src="https://1.bp.blogspot.com/-JhKvzDyvrtw/VsrlNFg87jI/AAAAAAAAH30/P3xO2CDputg/s400/Thunder%2Begg%2Bis%2Ba%2Bnodule-like%2Brock%2B-geology%2Bin.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Thunder egg is a nodule-like rock, similar to a filled<br />
geode, that is formed within volcanic ash layers.<br />
   credit: Bill The Eggman</td></tr>
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<br />
<span data-offset-key="aavig-0-0"><span data-text="true"><b>Geodes </b>are geological secondary structures which occur in certain sedimentary and volcanic rocks. They are themselves of sedimentary origin formed by chemical precipitation.</span></span><br />
<span data-offset-key="aavig-0-0"><span data-text="true"> <table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-D31nCQh1Jgw/VsmjdT5DstI/AAAAAAAAH3Y/Vpz-DW0MKsw/s1600/Inside%2Band%2Boutside%2Bviews%2Bof%2Bthe%2Bgeode%2B-geology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="261" src="https://1.bp.blogspot.com/-D31nCQh1Jgw/VsmjdT5DstI/AAAAAAAAH3Y/Vpz-DW0MKsw/s400/Inside%2Band%2Boutside%2Bviews%2Bof%2Bthe%2Bgeode%2B-geology%2Bin.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span class="mw-mmv-title">Inside and outside views of the geode</span></td></tr>
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<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><b>Geodes </b>differ from <b>vugs </b>in that the former were formed as early, rounded, structures within the surrounding rock and are often removed intact, whereas <b>vugs </b>are irregularly shaped pockets, voids or cavities within a formation, often along a vein or in breccia. <b>Geodes </b>also differ from "<b>nodules</b>" in that a nodule is a mass of mineral matter that has accreted around the nodule nucleus.</span></span></span></span><br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"> <table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-Y68ah-I1JSk/VsmiHMemheI/AAAAAAAAH3I/r7wq4XnM6P8/s1600/Thunder%2Begg%2Bagate%2B.%2BHead%2Bexplosion.%2BSo%2Bawesome%2Bfrom%2BNew%2BMexico.%2Bby%2BBill%2BThe%2BEggman%2B-geology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="288" src="https://2.bp.blogspot.com/-Y68ah-I1JSk/VsmiHMemheI/AAAAAAAAH3I/r7wq4XnM6P8/s400/Thunder%2Begg%2Bagate%2B.%2BHead%2Bexplosion.%2BSo%2Bawesome%2Bfrom%2BNew%2BMexico.%2Bby%2BBill%2BThe%2BEggman%2B-geology%2Bin.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="background-color: white; color: #141823; display: inline; float: none; font-family: "helvetica" , "arial" , sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.3199996948242px; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;">Thunder egg agate geode. from New Mexico. by Bill The Eggman</span></td></tr>
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<br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="8p6bm-0-0"><span data-text="true"><b>Geodes </b>can <b>form </b>in any cavity, but the term is usually reserved for more or less rounded formations in<i> igneous and sedimentary rocks.</i> They can form in gas bubbles in igneous rocks, such as vesicles in basaltic lavas; or, as in the American Midwest, in rounded cavities in sedimentary formations. After rock around the cavity hardens, dissolved silicates and/or carbonates are deposited on the inside surface. Over time, this slow feed of mineral constituents from <b>groundwater </b>or <b>hydrothermal </b>solutions allows crystals to form inside the hollow chamber.</span></span> </span></span></span></span> <br />
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<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-MIluHZ69PfI/VsmdY54nFjI/AAAAAAAAH2o/fuX7WUhWOTs/s1600/Huge%2Bpockets%2Bof%2Bamethyst%2Bcrystals%2Bwere%2Beverywhere%2Binside%2Bthe%2Bmine-geology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="301" src="https://1.bp.blogspot.com/-MIluHZ69PfI/VsmdY54nFjI/AAAAAAAAH2o/fuX7WUhWOTs/s400/Huge%2Bpockets%2Bof%2Bamethyst%2Bcrystals%2Bwere%2Beverywhere%2Binside%2Bthe%2Bmine-geology%2Bin.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span class="fbPhotosPhotoCaption" data-ft="{"tn":"K"}" id="fbPhotoSnowliftCaption" tabindex="0"><span class="hasCaption"><span dir="ltr">Large Vugs of amethyst crystals were everywhere inside the mine<br />
AMETHYST MINING. IN BRAZIL<br />
photo: <a href="http://lifeofsaturdays.com/" rel="nofollow nofollow" target="_blank">lifeofsaturdays.com</a></span></span></span></td></tr>
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</span></span></span></span><br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="8p6bm-0-0"><span data-text="true">Geode banding and <b>coloration </b>is the result of variable impurities. Iron oxides will impart rust hues to siliceous solutions. Most geodes contain clear quartz crystals, while others have purple amethyst crystals. Still others can have agate, chalcedony, or jasper banding or crystals such as calcite, dolomite, celestite, etc.</span></span> </span></span></span></span><br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="8p6bm-0-0"><span data-text="true"><b>Geodes </b>and geode slices are sometimes dyed with artificial colors. Samples of geodes with unusual colors or highly unlikely formations have usually been synthetically altered.</span></span> </span></span></span></span><br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"> <table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-i43WEVvrOwQ/VsmfRYVywpI/AAAAAAAAH24/0Yw40RYLXEE/s1600/Massive%2BAmethyst%2BGeode%2BFrom%2BGeology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://4.bp.blogspot.com/-i43WEVvrOwQ/VsmfRYVywpI/AAAAAAAAH24/0Yw40RYLXEE/s640/Massive%2BAmethyst%2BGeode%2BFrom%2BGeology%2Bin.jpg" width="480" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span class="irc_su" dir="ltr" style="text-align: left;">Massive Amethyst Geode From </span><span data-offset-key="1av7e-0-0"><span data-text="true">Uruguay</span></span></td></tr>
</tbody></table>
</span></span></span></span><br />
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</div>
<br />
<br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><b>Geodes </b>commonly have a chalcedony (<i>cryptocrystalline quartz</i>) shell lined internally by various minerals, often as crystals, particularly <i>calcite, pyrite, kaolinite, sphalerite, millerite, barite, celestite, dolomite, limonite, smithsonite, opal, chalcedony</i> and <i>macrocrystalline quartz</i>, which is by far the most common and abundant mineral found in <b>geodes</b>.</span></span> </span></span></span></span><br />
<br />
<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="8p6bm-0-0"><span data-text="true"><b>Geodes</b> are common in some formations in the United States (mainly in Indiana, Iowa, Missouri, western Illinois, Kentucky, and Utah). They also are common in Brazil, Uruguay,  Namibia, and Mexico.</span></span> </span></span></span></span> <br />
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<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/--cSeg8bJs2g/Vsmi0UGNZZI/AAAAAAAAH3Q/OiT0PF9L_Gk/s1600/Amethyst%2BGeode%2Binside%2Bthe%2Bground%2521%2Bgeology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="300" src="https://1.bp.blogspot.com/--cSeg8bJs2g/Vsmi0UGNZZI/AAAAAAAAH3Q/OiT0PF9L_Gk/s400/Amethyst%2BGeode%2Binside%2Bthe%2Bground%2521%2Bgeology%2Bin.jpg" width="400" /></a></td></tr>
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<span class="irc_su" dir="ltr" style="text-align: left;">Amethyst Geode inside Limestone rocks!</span></div>
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<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="8p6bm-0-0"><span data-text="true"><b>Geodes</b> are found mostly in basaltic lavas and limestones.</span></span> </span></span></span></span><br />
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<span data-offset-key="aavig-0-0"><span data-text="true"><span data-offset-key="1av7e-0-0"><span data-text="true"><span data-offset-key="8p6bm-0-0"><span data-text="true"><b>The world's largest known </b>crystal cave or vug is Crystal Cave, a celestine geode 35 feet (10.7 m) in diameter at its widest point, located near the village of Put-in-Bay, Ohio, on South Bass Island in Lake Erie.</span></span> </span></span></span></span><br />
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<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-VSw9I7LLIik/VsmkEP7G2NI/AAAAAAAAH3g/lwk4ddQ09gA/s1600/Empress%2Bof%2BUruguay-geology%2Bin.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://1.bp.blogspot.com/-VSw9I7LLIik/VsmkEP7G2NI/AAAAAAAAH3g/lwk4ddQ09gA/s400/Empress%2Bof%2BUruguay-geology%2Bin.jpg" width="250" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><i><span data-offset-key="1av7e-0-0"><span data-text="true">Empress of Uruguay</span></span></i></td></tr>
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<span data-offset-key="1av7e-0-0"><span data-text="true">The largest <b>amethyst geode</b> in the world is The ‘Empress of Uruguay’ Over three meters tall (that’s eleven feet) and weighing two and a half tonnes. It is located here in Atherton, North Queensland, Australia. </span></span></div>
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