page_title: Microspherulite
section_title: Other related terms
hierarchical_section_title: Microspherulite / Other related terms
caption_attribution_description: English: Glass spherical particles for use in industry
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: Pisolites are spheroidal particles, larger in size and commonly more distorted than ooids. The name derives from the Greek pisos (pea). Mineral concentrations (bauxites, limonites, siderites) and the pedogenic caliches (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 brines.
  Aerolite is a generic term indicating lithogenic elements gathered from the atmosphere. This term does not imply sphericity or microscopic size.
  Chondrules are the microscopic constituents of chondrites that represent 80% of the meteorites that fall to the Earth per the   Meteoritical Society. 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 pyroxene, surrounded by feldspars (crystalline or glassy); minor minerals are Fe-sulfide, metallic Fe-Ni and oxides.
  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 otolites (compounds of the vestibular system of the inner ear) and the calculi resulting from various histopathologies. Studies have confirmed that microorganisms are able to precipitate minerals.
  Pellets are those homogeneous aggregates with no internal structure, consisting of micritic calcite, spherical to ellipsoidal in shape and with sizes between 0.03 and 0.15 mm. They are thought to be faecal particles from aquatic organisms.
  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 emulsions, but it is also valid for water-air (hazes, drops) or other liquid fluids (oil-water).
  Carbonaceous microspherules are a type of soot particle floating in the atmosphere, produced by anthropogenic 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 graphite. The size ranges from tens to a hundred micrometres.
  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 (nanospheres), or 1 µm to 1000 µm (microspheres). 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.
caption: Figure 3: Solid glass microspheres used like ingredients in road and street signaling paintings.
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