A mineraloid is a naturally occurring substance that resembles a mineral, but does not demonstrate the crystallinity of a mineral. Mineraloid substances possess chemical compositions that vary beyond the generally accepted ranges for specific minerals, for example, obsidian is an amorphous glass and not a true crystal; lignite (jet) is derived from the decay of wood under extreme pressure underground; and opal is a mineraloid substance because of its non-crystalline nature. Pearl is a mineraloid substance because the calcite crystals and the aragonite crystals are bonded by an organic material, and naturally occurs without definite proportions of the components.
The first usage of the term mineraloid substance was in 1909, by mineralogist and geologist Julian Niedzwiedzki, in identifying and describing amorphous substances that resemble minerals.
Examples
Allophane, solid (IMA/CNMNC valid mineral name) Amber, non-crystalline structure, organic Anthracite or hard coal Bituminous coal Chlorophaeite Chrysocolla, solid (IMA/CNMNC valid mineral name) Deweylite, a mixture of serpentine and talc or stevensite Diatomite Ebonite, vulcanized natural or synthetic rubber (organic); lacks a crystalline structure Fulgurite, a variety of the mineraloid lechatelierite Jet, non-crystalline nature, organic (very compact coal) Lechatelierite, nearly pure silica glass, solid (IMA/CNMNC valid mineral name) Leonardite Libyan desert glass Lignite—brown coal Limonite, a mixture of oxides and hydroxides of iron Mercury, (as liquid) Moldavite Mookaite/Radiolarite Obsidian—volcanic glass; non-crystalline structure, a silica rich glass Opal, non-crystalline hydrated silica silicon dioxide, solid (IMA/CNMNC valid mineral name) Ozokerite, a black waxy hydrocarbon mixture Palagonite Pearl, organically produced carbonate Pele's hair Petroleum, liquid, organic Psilomelane Pumice, not counting those that are highly porphyritic such as from Mt. Pinatubo or those that have a high microlite content Pyrobitumen, amorphous fossilized petroleum (noncrystalline, organic) Shungite, black, lustrous, more than 98 weight percent of carbon Sideromelane, volcanic glass – non-crystalline, an iron rich, silica poor glass Tektite, meteoritic silica rich glass Water, e.g. as inclusions in other crystals, or in the form of rain, (as liquid) Zietrisikite, a mineral hydrocarbon wax
See also List of minerals – Mineraloids are listed after minerals in each alphabetically sorted section.
References
External links The Mineraloids Class. Amethyst Galleries.
de:Mineraloid he:מינרל#מינרלואידים