Maskelynite

Maskelynite is a glassy, non-crystalline form of plagioclase feldspar produced by shock metamorphism during meteorite impacts. It forms when rocks containing plagioclase are subjected to the high pressures and rapid cooling of an impact event, causing the crystalline feldspar to transform into a glass or to quench from a high-temperature melt. The exact mechanism can involve solid-state amorphization, partial melting, and rapid quenching within an impact melt sheet or breccia.

The mineralogical character of maskelynite is that it preserves the chemical composition of plagioclase but lacks long-range crystalline order. It often appears as glassy, colorless to pale grains intergrown with other minerals in impact-related rocks. Under transmitted light in petrographic sections, it is typically isotropic and does not show the birefringence associated with crystalline feldspars. Analytical techniques such as Raman spectroscopy, infrared spectroscopy, and electron microscopy help distinguish maskelynite from other glass types.

Occurrence and significance: Maskelynite is commonly associated with meteorite impact structures, including impact melt rocks, breccias, and some lunar and Martian samples. Its identification is used as a diagnostic indicator of shock metamorphism and an impact origin, helping to distinguish impact-related glasses from volcanic glasses such as obsidian or tektites. The presence and textural relationships of maskelynite can provide insights into the pressure-temperature history of the impact event.