Discovery of an Earthborn quasicrystal approximant

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Abstract Natural quasicrystals, compounds with characteristics intermediate between crystalline material and glass, have been so far discovered in extraterrestrial materials only. Further, their occurrence in nature is limited to metallic, Al-bearing alloys. The presence of metallic aluminum in these minerals raised doubts about their potential occurrence in terrestrial rocks. The geochemical conditions needed to form metallic Al are so reducing that they are considered very unlikely in a terrestrial environment. Given the report of dodecagonal symmetry in the synthetic Ta1.6Te quasicrystal, the search for terrestrial quasicrystals was focused on natural tellurides. Here, we report the discovery of the first terrestrial approximant of a dodecagonal quasicrystal, a Pd-Ni-telluride with formula Pd3Ni4Te8 and tetragonal symmetry, which was found as small inclusions in a rock sample coming from Kalgoorlie, Western Australia. Periodic approximants are crystalline materials that share a similar chemical composition with quasicrystals but have a slightly altered atomic structure, aligning their symmetry with the traditional principles of three dimensional crystallography. These crystalline approximants provide insights into the local atomic structure of their corresponding quasicrystals. Natural Pd3Ni4Te8 has been approved as a new mineral by the International Mineralogical Association with the name proxitwelvefoldite (IMA 2024-034). The Pd3Ni4Te8 composition has also been never reported to form quasicrystal approximants among synthetic products and could indicate the possible existence of a 12-fold quasicrystal in the Pd-Ni-Te system. The discovery points to the possibility that the quasicrystalline structure may be much more common than previously thought, even in non-alloy systems.