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Published December 2018 | public
Journal Article

Nuwaite (Ni_6GeS_2) and butianite (Ni_6SnS_2), two new minerals from the Allende meteorite: Alteration products in the early solar system

Abstract

Nuwaite (Ni_6GeS_2, IMA 2013-018) and butianite (Ni_6SnS_2, IMA 2016-028) are two new chalcogenide minerals, occurring as micrometer-sized crystals with grossular, Na-bearing melilite, heazlewoodite, and Ge-bearing Ni-Fe alloys in veins and as mono-mineralic crack-filling material in igneous diopside in the Type B1 Ca-Al-rich inclusion (CAI) ACM-2 from the Allende CV3 carbonaceous chondrite. The chemical composition of type nuwaite is (wt%) Ni 65.3, S 10.3, Ge 8.2, Te 7.9, Sn 5.1, and Fe 1.7, with a sum of 98.5 and an empirical formula of (Ni_(5.95)Fe_(0.16))(Ge_(0.60)Sn_(0.23))(S_(1.72)Te_(0.33)). The simplified formula is Ni6(Ge,Sn)(S,Te)2, leading to an end-member of Ni6GeS2. The chemical composition of type butianite is (wt%) Ni 62.1, Sn 8.9, Te 10.3, S 8.9, Ge 5.3, Fe 1.3, sum 99.1, giving rise to an empirical formula of (Ni_(5.93)Fe_(0.13))(Sn_(0.52)Ge_(0.41))(S_(1.56)Te_(0.45)). Butianite's simplified formula is Ni6(Sn,Ge) (S,Te)2 and the end-member formula is Ni6SnS2. Both nuwaite and butianite have an I4/mmm inter-growth structure with a = 3.65 Å, c = 18.14 Å, V = 241.7 Å^3, and Z = 2. Their calculated densities are 7.24 and 7.62 g/cm^3, respectively. Nuwaite and butianite are the first known meteoritic minerals with high Ge and Sn concentrations. Nuwaite and butianite are very late-stage, vapor-deposited, alteration products, filling in pores within preexisting grossular-rich alteration veins and cracks in igneous Al,Ti-diopside. These phases and associated heazlewoodite and Ge-bearing alloys are observed only within the Ca-,Al-rich inclusion (CAI) and not outside it or at the inclusion-matrix interface. As only sections in one half of ACM-2 contain nuwaite/butianite, they were probably derived through a relatively low f_(O2)-f_(S2) sulfidation process, in which a highly localized, low-temperature Ge-, Sn-bearing fluid interacted with a portion of the host CAI. It is likely that the fluid became relatively more Sn- and Te-enriched with time and that crack fillings post-date vein fillings, possibly due to a late remobilization of vein sulfides.

Additional Information

© 2018 Mineralogical Society of America. Manuscript received April 22, 2018; Manuscript accepted August 14, 2018; Manuscript handled by Steven Simon. SEM, EBSD, and EPMA analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065. J.R.B. acknowledges NASA grant NNG04GG14G. We thank Klaus Keil, Mike Zolensky, and associate editor Steven Simon for helpful reviews.

Additional details

Created:
August 19, 2023
Modified:
October 19, 2023