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    Ocean Volcanic Rocks Contain Samples of Recycled Crust

    Scientists have long believed that lava erupted from certain oceanic volcanoes contains materials from the early Earth’s crust. But decisive evidence for this phenomenon has proven elusive. New research from a team including Carnegie’s Erik Hauri demonstrates that oceanic volcanic rocks contain samples of recycled crust dating back to the Archean era 2.5 billion years ago. Their work is published in Nature. Oceanic crust sinks into the Earth’s mantle at so-called subduction zones, where two plates come together. Much of what happens to the crust during this journey is unknown. Model-dependent studies for how long subducted material can exist in the mantle are uncertain and evidence of very old crust returning to Earth’s surface via upwellings of magma has not been found until now. For more information about these results, see the press release from the Carnegie Institution.
Halite (rock salt) mineral
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Windows to the Universe/L.Gardiner

Halite

What’s that on your chips? It’s a mineral called halite! If you look closely at ordinary table salt, you will see that, just like other minerals, it looks like crystals. Halite is salt. In its natural form, it’s called rock salt.

Halite is found in sedimentary rocks. It is called an evaporite mineral because it formed in ancient seas and salt lakes as they slowly evaporated millions of years ago. As the water evaporated, thick deposits of salt were left behind. This process still goes on today. In fact, one way to get the halite used for table salt and road salt is to extract it from seawater by evaporating the water.

The sure way to determine if a mineral is halite is to taste it. However, don’t stick an unknown mineral sample in your mouth just in case it is poisonous. Instead, lick a finger and rub it against the mineral specimen that you think is halite. Then taste your finger so you don’t get too much of the mineral into your mouth.

  • Shape: Isometric (crystals usually look like cubes)
  • Luster: Glassy
  • Color: Clear, white, pinkish, or gray
  • Streak: White
  • Hardness: 2.5 on Mohs Hardness Scale
  • Cleavage: 3 planes of perfect cleavage
  • Fracture: Conchoidal

Last modified April 15, 2003 by Lisa Gardiner.

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TES XXVI, 3 fall 2010 The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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