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 a dense form of coal. Opal is another mineraloid due to its non-crystal nature. Pearls, considered by some to be a mineral due to 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.

A very common mineraloid is limonite a mixture of hydrated iron oxides.

Other naturally occurring substances that appear superficially to be minerals in nature are Nonminerals.

See also

• List of minerals Mineraloids are listed alphabetically after minerals.

Minerals

Mineraloid | Mineraloid | Mineralóide