a mineral-like substance that does not demonstrate crystallinity; their chemical compositions 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 naturally occurring, usually inorganic, solid consisting of either a single element or a compound, and having a definite chemical composition but lacking a systemic internal arrangement of atoms. See also mineral.

(min'-er-al-oid) A naturally occurring, usually inorganic solid that is not considered to be a mineral because it is amorphous, that is, it lacks a long-range three dimensional ordering of its structure.

a mineral -like substance that does not demonstratecrystallinity