page_title: Microspherulite
section_title: Aerial environment
hierarchical_section_title: Microspherulite / Classification / Aerial environment
caption_attribution_description: English: Iberulites are a particular type of microspherulites developed in the atmosphere and finally fallen to the earth's surface.
context_page_description: Microspherulites are microscopic spherical particles with diameter less than two mm, usually in the 100 micrometre range, mainly consisting of mineral material. Only bodies created by natural physico-chemical processes, with no contribution of either biological or human activity, are considered to be microspherulites.
  Generally speaking, the common feature indicates that each sphere represents an internal equilibrium of forces within a fluid medium.
context_section_description: Micrometeorites are typically metallic microspherules (iron or iron and nickel) but can also be formed by silicate minerals, whose dimensions must range from tens of micrometres to one millimetre. They correspond to pieces of extraterrestrial meteoroids, resulting from melting and vaporization during entry into the Earth’s atmosphere. During this melt stage a significant loss of mass can occur through holes in their surface. The degree of heating and their original composition determine that only a few minerals have been founded in micrometeorites. They have not yet been properly classified.
  Impact spherulites occur when a large extraterrestrial object strikes Earth at cosmic velocity, melts and vaporizes, silicate materials can condense into high spheroidal, sand-sized particles deposited around the point of impact. Unaltered impact spherulites consist entirely of glass (microtektites) or a combination of glass and crystals grown in flight (microkrystites). Primary crystals are only common in microspherulites from two Phanerozoic impact layers: the Upper Eocene microkrystite or clinopyroxene spherule layer  and the Cretaceous-Paleogene boundary (K/T boundary) layer.  Other crystalline phases may be olivine, Fe-rich pyroxene, spinels and feldspars. Frequently the crystals are replaced by diagenetic phases such as goethite, pyrite, glauconite, K-feldspars, quartz, sericite, chlorite, and carbonates.
  Iberulites are co-associations of well-defined minerals, together with non-crystalline compounds, with axial geometry and a characteristic depression (vortex), structured around a coarse-grained core with a smectite  rind, and pinkish colour (Figure 2). They are formed at present in the troposphere by complex aerosol-water-gas interactions. The modal size is in the 60-90 micrometre range, and the shapes are almost perfect spheres. Their name comes from the Iberian Peninsula, indicating the place where they were discovered.  They are related to intrusions of aerosol plumes from the Sahara desert. The mineralogy of the core (tens of micrometres thick) is commonly formed by quartz, calcite, dolomite  and feldspars, while the most frequent minerals of the rind (a few micrometres thick) are clay minerals, mainly smectites (beidellite, montmorillonite) and illite, amorphous silica  and impregnation of sulfate minerals   (mainly gypsum, alunite and jarosite) and chlorides.
caption: Figure 2: Group of iberulites observed under Scanning Electron Microscope (SEM). The arrows show vortex position.
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