Sequential Lonsdaleite to Diamond Formation in Ureilite Meteorites via In Situ Chemical Fluid/Vapor Deposition

• DOI: 10.1073/pnas.2208814119
• Publication Date: 2022-09-12T19:19:20Z
• Authors: Andrew G. Tomkins; Nicholas C. Wilson; Colin MacRae; Alan Salek; Matthew R. Field; Helen E. A. Brand; Andrew D. Langendam; Natasha R. Stephen; Aaron Torpy; Zsanett Pintér; Lauren A. Jennings; Dougal G. McCulloch
• Keywords: Physical Sciences; 01 natural sciences; 0105 earth and related environmental sciences

Ureilite meteorites are arguably our only large suite of samples from the mantle a dwarf planet and typically contain greater abundances diamond than any known rock. Some also lonsdaleite, which may be harder diamond. Here, we use electron microscopy to map relative distribution coexisting diamond, graphite in ureilites. These maps show that lonsdaleite tends occur as polycrystalline grains, sometimes with distinctive fold morphologies, partially replaced by + rims cross-cutting veins. observations provide strong evidence for how carbon phases formed ureilites, which, despite much conjecture seemingly conflicting observations, has not been resolved. We suggest pseudomorphic replacement primary shapes, facilitated supercritical C-H-O-S fluid during rapid decompression cooling. Diamond after via ongoing reaction gas. This > formation process is akin industrial chemical vapor deposition but operates at higher pressure (∼1-100 bar) provides pathway toward manufacture shaped application. It unique model ureilites can reconcile all relating formation.