A mineraloid is a mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amorphous glass and not a crystal. Jet is derived from decaying wood under extreme pressure. Opal is another mineraloid because of its non-crystal nature. Pearls, considered by some to be a mineral because of the presence of calcium carbonate crystals within their structure, would be better considered a mineraloid because the crystals are bonded by an organic material and there is no definite proportion of the components.

Common Mineraloids

  • Amber, organic, non-crystal structure.
  • Anthracite, a variety of coal, "hard coal."
  • Coal, organic, nonhomogeneous, and non-crystal structure.
  • Jet, not considered a true mineral due to organic, non-crystal nature, a mineraloid.
  • Lignite, a variety of coal, "Brown coal."
  • Limonite, amorphous hydrated iron oxide, a mineraloid.
  • Obsidian, volcanic glass - non-crystal structure.
  • Opal, non-crystal structure, a mineraloid.
  • Pearl, often considered a mineral due to crystal components, but then not a mineral due to organic origin, probably should be a mineraloid.
  • Petroleum, organic and liquid.
  • pyrobitumen, organic, nonhomogeous, non-crystal structure.
  • Vulcanite, vulcanized natural or synthetic rubber, thus not a mineral due to organic composition, lack of crystal structure, and not naturally occurring.

See also

  • List of minerals Mineraloids are listed after minerals in each alphabetically sorted section.

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