Tepkides

Tepkides are a term used in geology to describe a class of mineral-like particles embedded in volcanic tephra deposits. They are typically glassy or microcrystalline and may host small mineral inclusions. Tepkides form as fragments of eruptive glass rapidly quenched in the eruption column or on the ground, with secondary alteration that can lead to limited crystallization.

Etymology: The name derives from tephra, the volcanic ejecta, with the suffix -kide used in mineral nomenclature to indicate a mineral-like entity.

Occurrence: Tepkides have been reported in tephra-rich deposits worldwide, especially in pyroclastic flows, ash layers, and ignimbrites. They are often found as discrete grains within a finer glassy matrix.

Formation and structure: They originate from molten fragments that cool rapidly to a glassy state; subsequent diagenetic or low-grade metamorphic processes may promote crystallization of silica, feldspar, or oxides around a glassy core.

Physical properties: Tepkides are usually translucent to opaque, colorless to brown, with a glassy luster. The size ranges from tens of micrometers to a few millimeters. Hardness is typically around 5–6 on the Mohs scale for glassy varieties.

Classification and status: Tepkides are not universally recognized as formal mineral species in major databases. They are mainly used as descriptive terms in tephra studies to refer to glassy or near-glassy tephra particles with limited crystallization. Further research is needed to standardize criteria and nomenclature.

See also: Tephra, Tektite, Glass, Tephrochronology.