pseudomineral

A pseudomineral is a substance encountered in nature that resembles a mineral but does not meet the formal criteria used to define minerals in mineralogy. The term is used to describe materials that may appear mineral-like in field observations yet fail one or more foundational requirements for minerals.

Minerals are defined as naturally occurring, inorganic, crystalline solids with a definite chemical composition and an ordered internal atomic arrangement. Substances that do not meet these criteria—most commonly those that are amorphous (lacking long-range crystal order) or organic in origin—are often categorized as pseudominerals or mineraloids. The designation helps distinguish crystalline mineral species from non-crystalline, organic, or synthetic-like natural materials.

Common examples of materials that might be labeled pseudominerals include opal (a mineraloid lacking a true crystal lattice), obsidian (volcanic glass, an amorphous silica), and amber (fossilized organic resin). Some naturally occurring mixtures, such as certain limonite deposits, also do not have a single definite mineral composition and are treated as pseudominerals in some contexts. These substances can display mineral-like properties such as color, hardness, or luster, which can complicate field identifications without further analysis.

The term pseudomineral is not universally standardized. Many geologists prefer the term mineraloid for amorphous natural substances and reserve mineral status for crystalline, inorganic compounds with specific chemical compositions. The concept remains a practical descriptor in field geology and petrology to distinguish crystalline minerals from non-crystalline or organic natural materials. See also mineraloid, mineral, amorphous solid.