Project Description



The volcanic emissions, extremely varied, can be of two fundamental types from the point of view of the structure of the rock: lava material and pyroclastic material. The latter is highly conditioned by the presence of high amounts of gases that are expelled explosively and / or by gravitational collapse of eruptive columns and lava flows.

The pyroclastic material is very varied in size and can be classified into fragments thrown by the volcano in size from ash (<2 mm), lapilli (2-64 mm) and blocks (> 64 mm).

Pyroclastic rocks can be classified (Cas and Wright, 1992, Francis, 1996), based on genetic criteria such as:

  1. Pyroclastic Fall deposits, from materials violently expelled from the volcano (fragments of pumice and / or lapilli). They lack lamination within the layers but a certain «stratification» due to eruptive intermittence is well recognized. They are not frequent in all areas of Cabo de Gata, because the eruptions are shallow submarines
  2. Pyroclastic flow deposits, two types:
    1. Ignimbrite type deposit. In explosive eruptions lava is crushed in different sizes (pyroclastics) that move laterally on the slopes. «Clouds»  of hot gas and particles in suspension are also formed and deposited as volcanic ash. The ignimbrites are characterized by having what in geology is known as «fiames» or flames, which are lines that cross the rock in an elongated form, and may be composed of obsidian fragments, more or less altered and crushed, resulting from a process of crushing and welding the ashes and pumice upon depositing. Pumice is a clear vesicular vitreous fragment, from acid to intermediate magmas
    2. Pyroclastic surge type:. They are made of very fragmented materials, thick ash-sized. They present good lamination and stratification many times crossed. These deposits can be observed, for example, at the beach of Los Genoveses or the climb to Vela Blanca hill or the access road to the lighthouse of Cabo de Gata
  3. Hyaloclastites and autoclastic lithic breccias are two terms that are related to a sudden cooling and fragmentation of the volcanic material when entering the aquatic environment. Evidences of this rapid cooling are given by the occasional vitrification of the volcanic material. The gaps are easily differentiated by their chaotic character and abundant clasts. The hialoclastites are characterized by the presence of a very fine material. In the area you can recognize both materials in Cala Higuera and on the beach of Mónsul.
  4. Agglomerates- Lava Breccias. They are consolidated materials (pyroclastic rock). Originally they were pyroclastic materials that then slid very slowly giving a breccias look.
  5.  Epiclastic materials. Debris flow and mass flow deposits are also common in the area. These are sedimentary deposits that take place after the deposition of pyroclastic materials. They are deposits of avalanche type, chaotic with large blocks floating in a fine matrix (debris flow) or much finer (mass flow). Avalanche deposits originate from the collapse (most commonly in the form of a horseshoe) of the volcanic apparatus, due to a magmatic process or instability of the building (or a combination of both). In general, the material is transported dry.

Modified from:


The rocks called Bentonites and Zeolites originate as a result of the hydrothermal alteration of pyroclastic materials, as in the quarry of Frailes Este (deposit of zeolites of Los Murcianos), alternations of deposits of fall and base surge  as in Morrón de Mateo, or agglomerates and tuffs as in Los Trancos. It is estimated that the temperature of the hydrothermal fluids that originated the bentonites should be between 70ºC in the case of bentonites from the Sierra de Gata and about 40ºC in the case of the Serrata de Níjar, and that these fluids were of origin meteoric reheated. The recharge sources of the aquifers should be the Sierras Alhamilla and Cabrera, located at the N of the Sites (García-Romero, 2012).


Simplified scheme of bentonites and zeolites formation (Braga et al., 2003)


Chemical Composition

Pyroclastic materials (such as ignimbrites) are usually intermediate to acidic in composition. In the following diagram it is observed that the pyroclastic materials of the Caldera del Fraile have a dacitic composition (black cross), that is, with a high percentage in silica and intermediate in alkalis (Soriano et al., 2012).


The main compositional characteristics of bentonites and zeolites are summarized in the following tables (Reyes et al., 1987):


Main minerals and accessories

They normally show a microcrystalline matrix with amorphous minerals (glasses), with a quartz domain, biotite, plagioclase and glass particles. There are also pieces (pyroclastics) of other partially melted rocks and bombs / lapilli of the same eruption, as well as pumice pieces.

As for bentonites, the following table shows its composition:

Reyes et al., 1987


In general, according to Reyes et al. (1987), the phyllosilicates have average values of 86% and as accompanying minerals find plagioclase, quartz and calcite. The rest of the minerals that can appear do so in very low percentages. The fine fractions are formed almost exclusively by smectites (group of phyllosilicates that are partially clays) with small amounts of illite and interstratified illite / montmorillonite. Occasionally, zeolites appear along with the smectites, as occurs in the Los Escullos or Morrón de Mateo deposits, and in some cases they become the majority mineral, as occurs in the Los Murcianos deposit. The zeolite of this deposit corresponds to mordenite of high purity and the samples have a great compositional homogeneity


According to García-Romero (2012), the Bentonites have been exploited throughout the entire region, from Níjar to San José, passing through the Serrata de Níjar. More than 30 outcrops have been described, many of which have been exploited since the 1950s. These are open-pit bentonite quarries of excellent quality, with smectite percentages over 90%.

Location of the main bentonite and zeolite deposits of Cabo de Gata (Oyarzun et al., 2008).


Spain is the seventh producer of bentonitas of the European Union, behind Greece, Italy, Germany, Bulgaria, Czech R. and Cyprus. Its market is very broad. The expanded bentonite supplies more than 90% of the markets for absorbents, animal beds, civil engineering, drilling mud, sand casting, various applications in chemical manufacturing, iron pelletization, waterproofing and water treatment. In addition it supposes more than 70% of the bentonite sold for loads and as extenders. On the other hand, the undilated one is destined in 60% to clarification, discoloration and filtering of oils and fats, in inks, pesticides, pharmaceutical products and plastic applications (Panorama Minero, IGME). In recent years, its capacity as filling or sealing materials for the storage of radioactive waste has been studied.


Uses of Bentonites in 2005 (taken from Rodas).


According to the Panorama Minero (IGME, 2012), the production of bentonite in the province of Almeria in 2010 was 35,900 tons (table below). According to data from the Junta de Andalucía (Geological-Mining Information System of Andalusia – SIGMA) since 2007 the production of bentonites in Andalusia has increased, leaving five active farms, located in the province of Almeria with a production of 192,350 Tm. The majority of the production is exported (García-Romero, 2012).

Source: Mining Statistics of Spain. (Panorama Minero, IGME). Taken from García-Romero (2012).


The Los Murcianos zeolite deposit is the only Spanish deposit in operation. It is located near the coast, halfway between San José and Los Escullos, and is exploited by the company Minas Volcán (García-Romero, 2012).

Cabo de Gata-Nijar Geopark occurrences

Pyroclastic materials are widely represented throughout the Cabo de Gata, interstratified with lava materials (flows and domes).

Geological map of Cabo de Gata volcanic field (districts of Rodalquilar and San José). Lithologies: 1. Amphibolic Andesites. 2. Pyroclastic breccias and tuffs of amphibolic andesites. 3. Pyroxene Andesites. 4. Pyroxene Andesites with endogenous alteration. 5. Pyroclastic pyroxene andesite breccias. 6. Pyroclastic breccias of pyroxene andesite with endogenous alteration. 7. Lapilli or volcanic tuffs of pyroxene andesites. 8. Polygenic and tuff breccias of amphibole and pyroxene andesites. 9. Rhyolitic and dacitic breccias. 10. Rhyolitic and dacitic tuffs with endogenous alteration. 11. Andesite breccias. 12. Andesites breccias with strong alteration. 13. Dacites and amphibolic andesites. 14. Pycliclastic breccias of dacites and amphibole andesites. 15. Pyroclastic conglomerates and amphibolic dacite-andesite breccias with reddish matrix. 16. Pyroclastic and ignimbritic flows of the Cinto area with endogenous alteration. 17. Breccias of collapse of red-violet amphibole dacites. 18. Red-violaceous amphibole dacites with endogenous alteration. 19. Imitimbrite dacites with tuffs and basal ignimbrites with endogenous alteration (Las Lázaras unit). 20. Domes and flows of fine-grained quartz-amphibole dacites. 21. Dacitic and andesitic dams. 22. Shales, conglomerates, quartzites and limestones of the Maláguide complex. 23. Tertiary sediments. 24. Quaternary deposits. 25. Alluvial materials. 26. Dunes. (Taken from Rigol-Sánchez, 2000).



The bentonites and zeolites, according to the mineralogical and chemical characteristics of the bentonite, the deposits have been classified into three large groups (García-Romero, 2012):

  1.  Serrata de Níjar. There are numerous benthic zones: Cerro Colorado, Collado del Aire, Cortijo de Archidona, Pecho de los Cristos, Palma del Muerto.
  2. Northern Zone of the Sierra de Cabo de Gata. It contains the following sites: Mata Lobera, Rambla Vieja, Rincon de Agua Amarga, Rincón de las Caleras, Los Trancos, Jayón, Pozo Usero, La Valentina, Majada de las Vacas, Plomo, Cala Montoya, Bornos, Horicuelas.
  3. Southern Zone of the Sierra de Cabo de Gata. It contains the following sites: Cortijo de la Loma, Cerro Amatista, Los Escullos, Cortijo del Gitano, La Isleta del Moro, Morrón de Mateo, La Capitana, Las Hermanicas


Location map of the bentonite quarries of the Cabo de Gata region. ●: Bentonite quarry. MM: Morrón de Mateo. LT: The Trancos. CA: Cortijo de Archidona. (Caballero et al., 1985).




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