Jadeite and related species in shocked meteorites: Limitations on inference of shock conditions

Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Some-times, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)ᴹ²(Al)ᴹ¹(Si₂)ᵀO₆–(Ca)ᴹ²(Al)ᴹ¹(AlSi)ᵀO₆–(☐)ᴹ²(Si)ᴹ¹(Si₂)ᵀO₆ with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields (if any) and synthesis pathways, considered together with textural constraints, have different implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences casts a new light on many previous conclusions about the shock histories preserved in particular meteorites.