Latest Petrology Stories
The Associated Press DETROIT A meteorite resembling Michigan's Lower Peninsula has been sold at auction, but bidders weren't quite as smitten with the mitten as the seller expected . The 75-pound nickel-and-iron meteorite sold for $20,000 Sunday at Heritage Auction Galleries in Dallas. It had been expected to sell for $32,500 to $40,000. Michigan native Darryl Pitt, the meteorite's owner, says he is disappointed by the low price. He says he thinks the space rock is worth $50,000. There...
Study measures effects of chemical weathering on the composition of continentsNew research suggests that the geological staying power of continents comes partly from their losing battle with the Earth's oceans over magnesium. The research finds continents lose more than 20 percent of their initial mass via chemical reactions involving the Earth's crust, water and atmosphere. Because much of the lost mass is dominated by magnesium and calcium, continents ultimately gain because the lighter,...
A geologist from the University of Leicester has proposed an immense (1.5km) exhibition to illustrate the vastness of geological time and to give a vivid perspective of how quickly human activity is changing the climate. Sediments accumulate on deep ocean floors at a rate of a few centimeters every thousand years. The study of this "“ called stratigraphy "“ involves drilling vertically down into the sea bed to extract a sample core which gives a picture of continually changing life,...
PORT-OF-SPAIN, Trinidad -- A mud-spewing fissure in the ocean floor has given birth to a tiny Caribbean island and is posing a threat to small boats.The island, breaching a few inches above the ocean's surface and stretching 500 feet long, was discovered recently roughly five miles northeast of Trinidad, said Roderick Stewart, a seismologist at the University of the West Indies in St. Augustine.An advisory has been issued for small boats, which could lose buoyancy because of gas bubbling up...
Carbon dioxide, a greenhouse gas that has become a bane of modern society, may have saved Earth from freezing over early in the planet's history, according to the first detailed laboratory analysis of the world's oldest sedimentary rocks. Scientists have theorized for years that high concentrations of greenhouse gases could have helped Earth avoid global freezing in its youth by allowing the atmosphere to retain more heat than it lost. Now a team from the University of Chicago and the...
NASA -- A new study suggests the steps a planet must go through for complex animal life to arise. Clay made animal life possible on Earth, a UC Riverside-led study finds. A sudden increase in oxygen in the Earth's recent geological history, widely considered necessary for the expansion of animal life, occurred just as the rate of clay formation on the Earth's surface also increased, the researchers report. "Our study shows for the first time that the initial soils covering the...
Blacksburg, Va., Oct. 11, 2005Â -- Fluid inclusions "“ tiny bubbles of fluid or vapor trapped inside rock as it forms "“ are clues to the location of ores and even petroleum; and they are time capsules that contain insights on the power of volcanoes and hints of life in the universe. But the realization of the scientific value of fluid inclusions is relatively recent. At the Centennial Celebration Symposia for the Society of Economic Geologists, Virginia Tech Distinguished Professor of...
Jerusalem -- While we generally think of water in nature as a cool liquid that we can see -- streams, lakes, oceans -- there is a great deal of "hot fluid" activity taking place far out of sight, deep within the earth, that influences what ultimately takes place on the surface, including the amount of rainfall and the buildup of new land mass. What exactly is the nature of that hidden fluid deep beneath the surface and what changes does it undergo as it seeks an ever-deeper...
Mars is a rocky planet with an ancient volcanic past, but new findings show the planet is more complex and active than previously believed "“ at least in certain places. Finding those places, however, turns out to be trickier than just looking at landforms like river valleys or lakebeds or searching for specific minerals. "Context is everything," said Philip Christensen, Principal Investigator for the Thermal Emission Spectrometer (TES) on Mars Global Surveyor and for the Thermal...
Could Earth have had an even more violent infancy than previously imagined? New isotope data suggest that the Earth not only had a very violent beginning but also point to new information about our planet's chemical evolution.New and precise measurements of a neodymium isotope ratio (142Nd/144Nd) led Maud Boyet and Rick Carlson of Carnegie Institution's Department of Terrestrial Magnetism to the discovery that all terrestrial rocks have an excess of 142Nd compared to the expected building...
Latest Petrology Reference Libraries
Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. It is sometimes called "iron mica" and is found in granitic rocks, gneisses, and schists. Like other mica minerals, biotite has a highly perfect basal cleavage, its flexible sheets easily flaking off. It has a hardness of 2.5 - 3, a specific gravity of 2.7 - 3.1, is colored greenish to brown or black, and can be transparent to opaque. Biotite is occasionally found in large sheets, especially in...
Chert is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. It varies greatly in color from white to black, but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced forms respectively). It outcrops as nodules in limestone, chalk, and dolostone formations as a...
Chromite, iron magnesium chromium oxide: (Fe,Mg)Cr2O4, is an oxide mineral belonging to the spinel group. Magnesium is always present in variable amounts, also aluminium and iron substitute for chromium. Chromite is found in peridotite and other layered ultramafic intrusive rocks and also found in metamorphic rocks such as serpentinites. Ore deposites of chromite form as early magmatic differentiates. It is commonly associated with olivine, magnetite, serpentine, and corundum. Chromite is...
In geology, a conglomerate is a rock consisting of other stones that have been cemented together. Conglomerates are sedimentary rocks consisting of subangular clasts and are thus differentiated from breccias, which consist of angular clasts. Both conglomerates and breccias are characterized by clasts larger than sand (>2 mm). There are two varieties of conglomerate, defined by texture: paraconglomerates and orthoconglomerates. Paraconglomerates are one of two varieties of conglomerate...
Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), hornblende, and/or pyroxene. Varieties deficient in hornblende and other dark minerals are called leucodiorite. It is often described as "salt and pepper" when composed largely of light-colored minerals randomly interspersed with dark minerals. When olivine and more iron-rich augite are present, the rock grades into ferrodiorite, which is transitional to...
