A mineraloid is a naturally-occurring 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-crystalline nature. Pearl, considered by some to be a mineral because of the presence of calcium carbonate crystals within its 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, non-crystalline structure, organic
- Deweylite, a mixture of serpentine and talc or stevensite
- Ebonite, vulcanized natural or synthetic rubber (organic); lacks a crystalline structure
- Jet, non-crystalline nature, organic (very compact coal)
- Lechatelierite, nearly pure silica glass
- Limonite, a mixture of oxides and hydroxides of iron
- Mercury, liquid (IMA/CNMNC valid mineral name)
- Obsidian, volcanic glass – non-crystalline structure, a silica rich glass
- Opal, non-crystalline hydrated silica silicon dioxide (IMA/CNMNC valid mineral name)
- Pearl, organically produced carbonate
- Petroleum, liquid, organic
- Pyrobitumen, amorphous fossilized petroleum (noncrystalline, organic)
- Sideromelane, volcanic glass – non-crystalline, an iron rich, silica poor glass
- Shungite, black, lustrous, more than 98 weight per cent of carbon
- Tektites, meteoritic silica rich glass
- List of minerals – Mineraloids are listed after minerals in each alphabetically sorted section.
- Peacock, M. A.; Fuller, R. E. (1928). "Chlorophaeite, sideromelane, and palagonite from the Columbia River Plateau" (pdf). American Mineralogist. 13: 360–382. Retrieved 6 September 2017.
- Schandl, Eva S.; Gorton, Michael P. (1995). "Phyllosilicate Alteration of Olivine in The Lower Sheeted Dike Complex, Leg 140, Hole 504B" (PDF). Proceedings of the Ocean Drilling Program, Scientific Results. 137/140: 207–216. doi:10.2973/odp.proc.sr.137140.019.1995. ISSN 1096-7451.
- The Mineraloids Class. Amethyst Galleries.