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Murchisite, Cr (sub 5) S (sub 6) , a new mineral from the Murchison Meteorite

Chi Ma, John R. Beckett and George R. Rossman
Murchisite, Cr (sub 5) S (sub 6) , a new mineral from the Murchison Meteorite
American Mineralogist (December 2011) 96 (11-12): 1905-1908


Murchisite (IMA 2010-003), Cr (sub 5) S (sub 6) , is a new chromium sulfide mineral, discovered in the Murchison CM2 meteorite. The type material occurs as one subhedral crystal (1.3 X 4 mu m in size) in contact with low-Ni iron ("kamacite"), martensitic iron, schreibersite, and a Ca-,Al-rich glass, all of which are included in an isolated forsteritic olivine grain in the meteorite's matrix. The mean chemical composition determined by electron microprobe analysis of the type material is (wt%) Cr 53.32, S 42.87, V 1.44, Fe 1.14, P 0.10, Ni 0.10, sum 98.97. The empirical formula calculated on the basis of 6 S atoms is (Cr (sub 4.60) V (sub 0.13) Fe (sub 0.09) Ni (sub 0.01) ) (sub Sigma 4.83) (S (sub 6.00) P (sub 0.01) ) (sub S6.01) . Murchisite was also identified in another isolated olivine grain from the same meteorite. These crystals are subhedral to round in shape, 300 nm to 1 mu m in size, and occur in association with tochilinite and serpentine, within which it is included, chromite, and eskolaite. Its electron backscatter diffraction patterns are an excellent match to that of synthetic Cr (sub 5) S (sub 6) with the P31c structure, showing a = 5.982, c = 11.509 Aa, V = 356.67 Aa (super 3) , and Z = 2, based on previously published data from synthetic material. Murchisite is named for the locality (the Murchison meteorite). It is a low-temperature phase ( approximately 327 degrees C in the Cr-S system), probably formed from higher temperature Cr (sub 1-x) S exsolved or expelled from a Cr-, S-bearing, metal-rich spherule included in forsteritic olivine grains that were probably derived from chondrule fragments. The formation of this phase reflects sulfur fugacities intermediate between those that would have led to troilite and those that would have led to no sulfide at all. The high-temperature Cr (sub 1-x) S phase equilibrated with coexisting alloys to approximately 600 degrees C. Murchisite formed from this precursor at low temperatures (< approximately 300 degrees C) through ordering of S vacancies.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 96
Serial Issue: 11-12
Title: Murchisite, Cr (sub 5) S (sub 6) , a new mineral from the Murchison Meteorite
Affiliation: California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States
Pages: 1905-1908
Published: 201112
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 17
Accession Number: 2012-009961
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201205
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