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The huge geode of Pulpí



  The huge geode of Pulpí
The geode of Pulpí Photo credit: Hector Garrido

The Geode of Pulpí is an 11 meter long hollow ovoid with crystal-paneled walls. It's like the well-known stone clutches that are covered with bright crystallites, but so big that several people fit inside. The up to two-meter-tall crystals are so transparent that they look like ice crystals. Juan Manuel García-Ruiz and colleagues reveal in this essay for Geology the geological history that ended with the formation of the Pulpí Geode.

Like the giant crystals of Naica in Mexico (see the article by García-Ruiz and colleagues from 2007 Geology at pubs.geoscienceworld.org/gsa/g… cle / 35/4/327 / 1

29804 /) are the crystals of Pulpí gypsum (calcium sulfate with two water molecules). García-Ruiz says: "Uncovering their formation has been a very difficult task because unlike Naica, where the hydrothermal system is still active, the large geode of Pulpí is a fossilized environment."

The team conducted an investigation into the geology and geochemistry of the abandoned mine where the Geode was found, including a detailed mapping of the underground mining work used for the mine tourist visits.

They found that the Pulpi crystals formed at about 20 ° C, at shallow depths, where the temperature changes of the climate are still noticeable. These temperature variations, which are below the maximum solubility of gypsum (40 ° C), led to dissolution and recrystallization and enhanced a maturation process known as Ostwald ripening.

  •   The Giant Geode of Pulp & # 237;
    The Mina Rica in the Sierra del Aguilón, Pulpí, Almeria. Picture credits: Javier Trueba
  •   The giant geode of pulp
    The team in the mine. Picture credits: Hector Garrido

García-Ruiz: "This roughly corresponds to the temperature cycles in the control of crystal quality in industrial processes." A continuous supply of salt to form the crystals was made by dissolving anhydrite (the anhydrous form of calcium sulfate), the mechanism responsible for the formation of the large Naica crystals.

Due to their purity, the crystals are crystals. The formation of the geode can not be dated exactly. Indirect constraints are possible, however: "They certainly grew after 5.6 million years of desiccation of the Mediterranean, most likely less than two million years but more than 60,000 years old, as this is the age of the carbonate crust, one of the great gypsum crystals "García-Ruiz says.


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Further information:
The origin of large gypsum crystals in the geode of Pulpí (Almería, Spain) pubs.geoscienceworld.org/gsa/g… rystals-in-the-Geode

Provided by
Geological Society of America




Quote :
The Giant Geode of Pulpí (2019, October 15)
retrieved on October 16, 2019
from https://phys.org/news/2019-10-giant-geode-pulp237.html

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