Iberulites are a particular type of
microspherulites (Fig. 1) that develop in the atmosphere (
troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. Fro ...
), finally falling to the earth's surface. The name comes from the
Iberian Peninsula
The Iberian Peninsula (),
**
* Aragonese and Occitan: ''Peninsula Iberica''
**
**
* french: Péninsule Ibérique
* mwl, Península Eibérica
* eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, def ...
where they were discovered.
[Díaz-Hernández, J.L. (2000)]
Aportaciones sólidas a la atmósfera originadas por un incendio forestal en el ámbito mediterráneo
''Estudios Geológicos'', 56: 153–161
Definition
An iberulite is a ''co-association''
[Berstch P. M. y Seaman J. C. (1999). ]
Characterization of complex mineral assemblages: implications for contaminant transport and environmental remediation
�. ''Proceedings National Academy of Sciences USA'', 96: 3350–3357 with
axial
Axial may refer to:
* one of the anatomical directions describing relationships in an animal body
* In geometry:
:* a geometric term of location
:* an axis of rotation
* In chemistry, referring to an axial bond
* a type of modal frame, in music
* ...
geometry, consisting of well-defined mineral grains, together with non-crystalline compounds, structured around a
coarse-grained
Granularity (also called graininess), the condition of existing in granules or grains, refers to the extent to which a material or system is composed of distinguishable pieces. It can either refer to the extent to which a larger entity is sub ...
core with a
smectite rind, only one
vortex
In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in ...
and pinkish color (Figs. 1-2), formed in the troposphere by complex
aerosol
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of anthropogen ...
-water-gas interactions.
Shape
These microspherulites are mostly spherical in shape (roundness index=0.95), with 60-90 μm modal diameter, although some particles can be up to 200 μm in diameter.
[Díaz-Hernández, J.L. y Párraga (2008) ]
The nature and tropospheric formation of iberulites: Pinkish mineral microspherulites
�. ''Geochimica et Cosmochimica Acta'', 72: 3883–3906 According to this roundness index, these microspherules are really elongated spheroids with two axes defined along a polar plane and typically presenting a depression or vortex. The presence of plant filaments in the atmosphere can distort these shapes and sizes. In any case, these are uncommon “giant” aerosol particles.
Compositional attributes
Composition can be determined by both X-ray diffraction (XRD) and electronic microscopy techniques (mainly SEM, EDX, HRTEM). Sections show that the body of iberulites can be divided into core and rind. The core is mainly formed by grains of
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...
,
calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...
,
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
and
feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
s. The rind shows
clay minerals
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.
Clay minera ...
, mainly
smectites (beidellite,
montmorillonite) and
illite, as well as
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
s, chlorides and amorphous
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
. The latter group of minerals could be the result of neoformations during the maturation process occurring in the atmosphere during the final stages of iberulite formation. It is striking that sulphates only appear in the periphery of the iberulites.
[Díaz-Hernández, J.L. y Párraga (2008) ]
The nature and tropospheric formation of iberulites: Pinkish mineral microspherulites
�. ''Geochimica et Cosmochimica Acta'', 72: 3883–3906 Flight over areas with anthropogenic or natural (volcanic, as those of North Atlantic archipelagos) sulphur emissions probably adsorbs
SO2 onto the iberulite surface. Descent to the ''marine boundary layer'' (MBL)
[Kloesel, K. A. y Albrecht, B. A. (1989). ]
Low-level inversions over the tropical Pacific. Thermodynamic structure of the boundary layer and the above inversion moisture structure
�. ''Monthly Weather Review'', 117: 87-101 of the Iberian-Moroccan Atlantic coast leads to the incorporation of
sea salt and microorganisms. The iberulites eventually fall on the southern Iberian Peninsula, where they have been detected.
Formation
Geographical setting
Iberulites have as yet only been found in the southern Iberian Peninsula. This location is geographically close to North Africa and it is therefore influenced by the emissions of Saharan aerosols, which are the greatest contributor of particulate matter to the atmospheric global dust budget
[Tanaka T.Y. and Chiba M. (2006). A numerical study of the contributions of dust source regions to the global dust budget. Global Planetary Change 52, 88-104, ]
� (Fig. 3).
Saharan dust outbreaks and iberulites
The general content of aerosols in the atmosphere of the southern Iberian Peninsula is clearly related to the evolution of aerosols arriving from North Africa.
[Diaz-Hernandez J.L. and Sanchez-Navas A. (2016). Saharan dust outbreaks and iberulite episodes. Journal of Geophysical Research: Atmospheres 121, 7064-7078, https://doi.org/10.1002/2016JD024913] Monitoring of dry aerosol deposition using passive samplers determined the formation of iberulites in two periods of the year (Fig. 4). The main depositional period occurs throughout the summer, while the second appears as a minor peak in early spring. However, the formation of iberulites is more specifically related with Saharan dust outbreaks, or dust plumes (Fig. 5) occurring within these two defined periods.
[Diaz-Hernandez J.L. and Sanchez-Navas A. (2016). Saharan dust outbreaks and iberulite episodes. Journal of Geophysical Research: Atmospheres 121, 7064-7078, https://doi.org/10.1002/2016JD024913]
Iberulites and red rains
Short episodes of wet deposition (more specifically red rains) were observed
[Diaz-Hernandez J.L. and Sanchez-Navas A. (2016). Saharan dust outbreaks and iberulite episodes. Journal of Geophysical Research: Atmospheres 121, 7064-7078, https://doi.org/10.1002/2016JD024913] during Saharan dust outbreaks over the period 2004-2013. Monitoring of these episodes led to the obtaining of a sequence of droplet impacts (Fig. 6) corresponding to June 6, 2012. This sequence would have begun with the formation of more or less aerosol-rich water droplets (or precursor water droplets
[Pruppacher H. R. and Klett J. D. (1997). Microphysics of clouds and precipitation (2nd ed.). Dordrecht: Kluwer Academic Publishers. 954 pp. ]) (Fig. 6A). The aerosol contents, together with dissolved salts (detected in this sequence as whitish or shiny precipitates), would have gradually increased, finally producing a well-defined iberulite after desiccation (Fig. 6E).
The passage of these Saharan dust outbreaks over the study site had a total mean duration of five days (Fig. 7). It was observed during this passage that the central day presented the highest air temperatures and PM
10 and PM
2.5 (PM
10>PM
2.5) contents, whereas relative humidity decreased (RH). A relation was therefore established between monthly numbers of iberulite episodes and PM
10 content-RH, which determined that clean atmospheres (<5 μg•m-3) with RH>65% do not present suitable conditions for iberulite formation.
[Diaz-Hernandez J.L. and Sanchez-Navas A. (2016). Saharan dust outbreaks and iberulite episodes. Journal of Geophysical Research: Atmospheres 121, 7064-7078, https://doi.org/10.1002/2016JD024913]
Stages in the formation of iberulites
Iberulites are linked to the evolution of high-dust air masses (plumes) which, originating in Saharan dust storms, are transported over the Iberian Peninsula and often across the eastern North Atlantic Ocean. These plumes occur in the warm season (May to September), as a result of anticyclone activity affecting the Iberian Peninsula, and only sporadically in spring.
Based on the relation between iberulites and red rain events, as well as the morphologies and compositional attributes observed, an aqueous interphase hypothesis has been suggested as the unitary mechanism for tropospheric formation of iberulites.
[Díaz-Hernández, J.L. (2000)]
Aportaciones sólidas a la atmósfera originadas por un incendio forestal en el ámbito mediterráneo
''Estudios Geológicos'', 56: 153–161[Díaz-Hernández, J.L. y Párraga (2008) ]
The nature and tropospheric formation of iberulites: Pinkish mineral microspherulites
�. ''Geochimica et Cosmochimica Acta'', 72: 3883–3906[Diaz-Hernandez J.L. and Sanchez-Navas A. (2016). Saharan dust outbreaks and iberulite episodes. Journal of Geophysical Research: Atmospheres 121, 7064-7078, https://doi.org/10.1002/2016JD024913]
Interactions between water droplets and Saharan aerosols create complex hydrodynamic conditions
[Pruppacher H. R. and Klett J. D. (1997). Microphysics of clouds and precipitation (2nd ed.). Dordrecht: Kluwer Academic Publishers. 954 pp. ] causing the possibility of collisions (wake capture and front capture) that originate the "precursor water droplets" of the iberulites.
[Díaz-Hernández, J.L. (2000)]
Aportaciones sólidas a la atmósfera originadas por un incendio forestal en el ámbito mediterráneo
''Estudios Geológicos'', 56: 153–161[Díaz-Hernández, J.L. y Párraga (2008) ]
The nature and tropospheric formation of iberulites: Pinkish mineral microspherulites
�. ''Geochimica et Cosmochimica Acta'', 72: 3883–3906[Diaz-Hernandez J.L. and Sanchez-Navas A. (2016). Saharan dust outbreaks and iberulite episodes. Journal of Geophysical Research: Atmospheres 121, 7064-7078, https://doi.org/10.1002/2016JD024913]
The movement of these water droplets to lower tropospheric levels implies either simultaneous or consecutive processes such as coalescence, formation of vortex and downdraught. During this phase the iberulites acquire their spherical shape and internal structure (core and rind), although sometimes this shape can be distorted.
There is an additional process of atmospheric maturation of iberulites that, in detail, only happens on the smectite rind, by means of
Heterogeneity, heterogeneous and multiphase reactions producing sulfates as the result of
H2SO4 attack on the minerals of the rind. This would lead to the rapid transformation of some primary minerals into products of atmospheric neoformation secondary minerals): the sulfates (mainly the
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
) would be the product of H
2SO
4 attack on the interlayer cations of the smectites, which would gradually destroy the octahedral and tetrahedral sheets of
phyllosilicates
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually consid ...
creating mixed sulfates.
The
alunite
Alunite is a hydroxylated aluminium potassium sulfate mineral, formula K Al3( S O4)2(O H)6. It was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum. First called ''aluminilite'' by J.C. D ...
-
jarosite
Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe3(SO4)2(OH)6. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct d ...
found in the smectite rind would have a similar origin. If acid attack progresses further, the phyllosilicate grains would be completely destroyed, producing amorphous silica and releasing
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
. Since
biogenic
A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of p ...
exoskeletons have no signs of
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
, they must have been incorporated after the acid attack described above, probably simultaneously with the incorporation of sea salt.
See also
*
Aerosol
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of anthropogen ...
*
Dust storm
A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transp ...
*
Mineral dust
*
Plume
*
Red rain in Kerala
*
Saharan Air Layer
*
Troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. Fro ...
Notes
References
External links
*{{Commonscatinline
Mineralogy
Atmospheric sciences