¹Paul D. Asimow, ²Chaney Lin, ^3,4Luca Bindi, ¹Chi Ma, ^5,6Oliver Tschauner, ⁷Lincoln S. Hollister,⁸Paul J. Steinhardt
Proceedings of the National Academy of Sciences 113 7077–7081 Link to Article [doi: 10.1073/pnas.1600321113]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125;
²Department of Physics, Princeton University, Princeton, NJ 08544;
³Dipartimento di Scienze della Terra, Università degli Studi di Firenze, I-50121 Firenze, Italy;
⁴Consiglio Nazionale delle Ricerche–Istituto di Geoscienze e Georisorse, Sezione di Firenze, I-50121 Firenze, Italy;
⁵Department of Geoscience, University of Nevada, Las Vegas, NV 89154;
⁶High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89154;
⁷Department of Geosciences, Princeton University, Princeton, NJ 08544;
⁸Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544

We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe2+0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68–73Fe11–16Cu10–12Cr1–4Ni1–2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

¹Richard V. Morris et al. (>10)*
Proceedings of the National Academy of Sciences (2016) 113 7071-7076 Link to Article [doi:10.1073/pnas.1607098113]
¹NASA Johnson Space Center, Houston, TX 77058
*Find the extensive, full author and affiliation list on the publishers Website

Tridymite, a low-pressure, high-temperature (>870 °C) SiO₂ polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO₂ (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO₂ glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides−perchlorates−chlorates), and has minor TiO₂ and Fe₂O₃T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a “Lake Gale” catchment environment can account for Buckskin’s tridymite, cristobalite, feldspar, and any residual high-SiO₂ glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO₂ glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.