What is a Mineraloid?

Definition of a Mineraloid

A mineraloid is a naturally occurring, inorganic substance that has no internal crystalline structure. In other words, during its formation, no crystals have grown.

Minerals, on the other hand, are crystalline, meaning they're made up of crystals.

Naturally occurring crystalline solids are made up of a highly ordered, repeating arrangement of atoms. In a non-crystalline solid, atoms do not come together in this way and instead form a pattern that's random or disorganised.

Minerals and mineraloids have a definite chemical composition and form through natural geological processes.

Examples of mineraloids include obsidian, opal, amber, tektites (moldavite), shungite and pearl. 

It can be difficult to distinguish a mineraloid from a mineral based on appearance alone because both can have similar physical characteristics, such as colour, lustre, and texture.

The word 'amorphous' is often used instead of 'mineraloid', however, the meaning is slightly different.

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A mineraloid is a naturally occurring substance that may look like a mineral but does not have a crystalline structure. 'Amorphous' is a broader term that describes any material, natural or otherwise, that is non-crystalline.

The word amorphous is used in various scientific fields to describe a substance that lacks a definite crystalline structure or well-defined shape. 

'Amorphous' comes from the Greek 'a', meaning 'without' or 'not', and 'morphē', meaning 'form' or 'shape.' When combined, 'a' and 'morphē' create 'amorphos', which translates to 'shapeless' or 'without form'.

Article Pictures

Precious opal - Courtesy of James St. John. Amber, obsidian, and moldavite courtesy of Stan Celestian.