450:). They may be made up of organic-inorganic compounds and provided with different properties. In fact, commercially, microspheres can be found manufactured from materials such as glass, polymers (polyethylene, polystyrene) or ceramic. Microspheres can be solid or hollow, and so their density will be very different as well as their applications. Hollow microspheres usually are added to reduce the density of a material. Solid microspheres have numerous applications depending on their size and their manufacture material. Solid glass microspheres are used in fields such as roads and streets signaling (Figure 3). They are added to paintings used for traffic signs and roadway surface signaling to incorporate the retroreflective effect. So they improve the night visibility of the way.
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343:(subaerial environment) can have pisolitic structure. They usually reach 5–8 mm in diameter and for this reason they can not strictly be considered microspherulites. Dunham (1969) considered them associated to caliches, while Pray and Esteban (1977) suggested they were formed by inorganic precipitation from
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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
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of material in solution, much as salt crystallizes from water during evaporation. In the former case they have thin concentric layers, and in the latter they have radiating sprays of crystals. However, a combination of both processes can be found. Microbes could contribute to their
147:. 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.
367:. Chondrules range in diameter from a few micrometres to over 1 cm. They are formed by rapid heating of solid precursor material and subsequent melting, followed by slow cooling. Their main composition is silicate minerals such as olivine and
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facies
Permian Reef complex, Guadalupe Mountains, New Mexico and West Texas. 1977 Field Conference Guidebook. Society of Economic Paleontologists and Mineralogists, Permian Basin Section, Publication 77-16: 479-483.
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Glass, B.P., Burns, C.A., Crosbie, J.R., DuBois, D.L., 1985. Late Eocene North
American Microtektites and Clinopyroxene-Bearing Spherules, Proceedings of the Sixteenth Lunar and Planetary Science Conference. Part 1.
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Verrecchia, E.P., Freytet, P., Verrecchia, K.E., Dumont, J.L., 1995. Spherulites in calcrete laminar crusts: biogenic CaCO3, precipitation as a major contributor to crust formation. J. Sed. Research A65, 690–700.
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Dunham, R.J., 1969. Vadose pisolites in the
Capitan Reefs (Permian) New Mexico and Texas, in Depositional Environments in carbonate rocks: Soc. Econ. Palaeontologists and Mineralogists Spec. Publ. 14, 182-191.
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Artefacts are spherules intentionally produced spherical particles for use in industry or medicine. The shape is often perfectly spherical, truly uniform and size ranging ~ 50 nm to 1000 nm (
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combustion processes of fuels, and may be coated with a layer of adsorbed hydrocarbons, sulfates or both. These particles are hollow microspherules that are black in colour, and made up of carbon or
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Biolites are biologically produced, many organisms can produce mineral particles dubbed in general biolites. Their shape, size and composition may be very varied. As examples we can cite
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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
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Bubbles include frequently unstable spherules which may be produced by the dispersion of two immiscible fluids forming an emulsion. Usually this term is applied to air-water
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DĂaz-Hernández, J.L., Párraga, 2008. The nature and tropospheric formation of iberulites: Pinkish mineral microspherulites. Geochimica et
Cosmochimica Acta 72, 3883–3906.
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DĂaz-Hernández, J.L., 2000. Aportaciones sĂłlidas a la atmĂłsfera originadas por un incendio forestal en el ámbito mediterráneo. Estudios GeolĂłgicos 56, 153–161.
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are microscopic spherical particles with diameter less than two mm, usually in the 100 micrometre range, mainly consisting of mineral material (the Greek
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Aerolite is a generic term indicating lithogenic elements gathered from the atmosphere. This term does not imply sphericity or microscopic size.
253:-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
116:(egg). They are formed by growing larger and accreting material as they move around. They accomplish this either (a) by physical attachment of
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Smit, J., 1999: The global stratigraphy of the. Cretaceous-Tertiary boundary impact ejecta. Annu. Rev. Earth
Planetary Science, 27: 75-113.
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this contribution is possible) or human activity, are considered to be microspherulites. Generally speaking, the common feature (
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Several types of these forms are found in nature. Depending on the formational environment, microspherulites can be classed as
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Pisolites are spheroidal particles, larger in size and commonly more distorted than ooids. The name derives from the Greek
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means "stone"). Only bodies created by natural physico-chemical processes, with no contribution of either biological (in
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Figure 2: Group of iberulites observed under
Scanning Electron Microscope (SEM). The arrows show vortex position.
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Micrometeorites are typically metallic microspherules (iron or iron and nickel) but can also be formed by
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Figure 3: Solid glass microspheres used like ingredients in road and street signaling paintings.
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Esteban, M., Pray, L.C., 1977. Origin of the pisolite facies of the shelf crest. In: Upper
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material as they roll around, much in the manner of a snowball, and (b) by the
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rind, and pinkish colour (Figure 2). They are formed at present in the
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Figure 1: Oolites observed with a transmitted light microscope.
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Oolites are internally structured spheres, composed mainly by
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355:Chondrules are the microscopic constituents of
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455:References
373:Fe-sulfide
361:meteorites
357:chondrites
235:Iberulites
219:carbonates
197:glauconite
185:diagenetic
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333:limonites
311:chlorides
275:feldspars
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71:aerolites
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384:otolites
369:pyroxene
341:caliches
329:bauxites
307:jarosite
297:(mainly
271:dolomite
243:smectite
215:chlorite
211:sericite
189:goethite
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390:of the
303:alunite
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251:aerosol
177:spinels
169:olivine
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377:oxides
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