Crystal structures of members of the cupropavonite homologous series with ideal composition AgCu2PbBi5S10: cupropavonite (5,5)( 5,5P) and cupropavonite (4,6) ( 4,6P)
Mumme, William G.; Gable, Robert W.; Wilson, Nick
published: Jan 1, 2015
ArtNo. ESP154019201007, Price: 29.00 €
Two structural variants of minerals with the ideal composition AgCu2PbBi5S10 have been found in the one crystal obtained from a specimen of USNM92902, which is the type specimen of berryite, Hall's Valley, Park County, Colorado, held at the Smithsonian National Museum of Natural History. Both have the unit cell a = 13.3551(6), b = 4.0064(2), c = 32.7835(17) Å, β = 93.397(4)°, space group C2/m. Crystal structure analysis has shown one to have a structure represented by the notation 5,5P used to designate members of the pavonite, or in this case, cupropavonite homologous series. Regular alternation of pavonite-like layers with N = 5 occur in this structure. The other structure may be represented by the notation 4,6P, because, in this case, pavonite-like layers with N = 4 and N = 6 alternate in the structure. This results in them both having the same ideal composition and unit cell of previously defined for cupropavonite. At this stage for ease of reference, and discussion, 5,5P is called cupropavonite (5,5), and 4,6P is called cupropavonite (4,6). This is to retain (some) consistency with the guidelines presented for mineral names by the Commission on New Minerals and New Mineral Names (CNMMN) in their example of nomenclature for variable-fit homologous series. Density Functional Theory analysis of the structures indicate both to be stable, with 5,5P somewhat more so than 4,6P.