Mineraloid

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 is considered a mineraloid because the included calcite and/or aragonite crystals are bonded by an organic material, and there is no definite proportion of the components.

Examples[]

Allophane, solid (IMA/CNMNC valid mineral name)
Amber, non-crystalline structure, organic
Anthracite or hard coal
Bituminous coal
^[1]
Chrysocolla, solid (IMA/CNMNC valid mineral name)
, a mixture of serpentine and talc or ^[2]
Diatomite
Ebonite,^{[citation needed]} 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, or brown coal
Limonite, a mixture of oxides and hydroxides of iron
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^[1]
Pearl, organically produced carbonate
Pele's hair
Petroleum, liquid, organic
Psilomelane
Pumice
Pyrobitumen, amorphous fossilized petroleum (noncrystalline, organic)
Shungite, black, lustrous, more than 98 weight percent of carbon
Sideromelane,^[1] volcanic glass – non-crystalline, an iron rich, silica poor glass
Tektite, meteoritic silica rich glass
Water, e. g. as inclusions in other crystals, liquid
Zietrisikite, a mineral hydrocarbon wax