Mineraloid

A mineraloid is a naturally occurring, solid, inorganic substance that resembles a mineral but does not exhibit the crystalline structure characteristic of minerals. Mineraloids lack the long-range, ordered atomic arrangement found in true minerals. This absence of crystalline structure can arise from various factors, including rapid cooling of volcanic glass, lack of sufficient time for crystal formation, or the presence of amorphous compounds. While they share many physical properties with minerals (e.g., hardness, luster, density), their internal atomic arrangements are disordered, leading to their classification as mineraloids. Examples are natural glass obsidian, which is volcanic in origin and its rapid cooling inhibits the formation of a crystal structure.

Mineraloid meaning with examples

• Obsidian, a volcanic glass formed from rapidly cooled lava, is a common mineraloid. It's visually striking, but its lack of crystal structure differentiates it from crystalline minerals. Obsidian's amorphous nature results from the molten rock solidifying too quickly for crystals to organize themselves. Consequently, it does not cleave or fracture in regular patterns.
• Amber, fossilized tree resin, is sometimes considered a mineraloid. Although organic in origin, it is a naturally occurring solid that can be mistaken for a mineral due to its hardness and vitreous luster. The lack of a definite crystalline structure, and its organic components, classify amber among the mineraloids.
• Opal, a hydrated silica mineraloid, presents a kaleidoscopic display of colors due to the diffraction of light. Unlike quartz crystals, opal's silica spheres are arranged in a semi-ordered pattern, leading to its classification as a mineraloid rather than a mineral. The light interaction inside the spheres of the opal causes an iridescence.
• Limonite, a hydrated iron oxide, often forms as a mineraloid. It is an earthy material that lacks a clear crystalline structure. It is frequently found in areas where iron minerals have been weathered. It often appears in botryoidal or massive form, showing no crystal faces, characteristic of mineraloids.