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