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, non-crystalline structure
  • Jet, non-crystalline nature, very compact coal
  • Native mercury, liquid, IMA/CNMNC valid mineral name
  • Lechatelierite, nearly pure silica glass
  • Limonite, a mixture of oxides
  • Lapis Lazuli, a mix of minerals
  • Obsidian, volcanic glass - non-crystalline structure, a glass and quartz mixture
  • Opal, non-crystalline silicon dioxide, a mix of minerals, IMA/CNMNC valid mineral name
  • Pearl, organicly produced carbonate
  • Petroleum, liquid
  • Pyrobitumen, non-homogeneous, non-crystalline structure, doesn't melt by heating
  • Vulcanite, vulcanized natural or synthetic rubber, thus not a mineral due lack of crystalline structure
  • Tektites, meteoritic silica glass

See also