Minutite

Minutite is a hypothetical ultrafine-grained igneous rock that, if it existed, would be characterized by a crystal size of less than 0.01 millimeters. The term is derived from "minute," referring to its exceedingly small grain size, and the suffix "-ite," commonly used for rock types. This grain size would be so small that individual mineral crystals would be largely indistinguishable even under a standard optical microscope, appearing more like a cryptocrystalline or glassy groundmass. Rocks with extremely fine grains are typically formed by rapid cooling of magma, a process known as quenching. Such rapid cooling prevents the atoms from organizing into larger crystal structures. While a theoretical concept, rocks with grain sizes approaching this theoretical limit are found in nature, often as a component of volcanic rocks that have cooled very quickly. Examples include certain types of basalt, rhyolite, and obsidian, though these are usually described with terms that reflect their actual observed grain size, such as aphanitic or glassy. The concept of minutite serves as a theoretical endpoint in the classification of igneous rock textures based on grain size.