20_1326lbonazzi

• Main Authors: Paola Bonazzi, Luca Bindi, Valentina Popova, Giovanni Pratesi, Silvio Menchetti
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2003
• Subjects: Kamchatka
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1062.6682; http://rruff.info/rruff_1.0/uploads/AM88_1796.pdf

ABSTRACT Alacranite from the type locality (Uzon caldera, Kamchatka, Russian Federation) was submitted for structural analysis. A single crystal was selected and the following lattice parameters were determined: a = 9.942(4), b = 9.601(2), c = 9.178(3) Å, b = 101.94(3)∞, V = 857.1 (5) Å 3 . The crystal structure was solved in the P2/c space group using direct methods and refined to R = 6.79% for 472 observed reflections. The structure of alacranite consists of an ordered sequence of As 4 S 4 and As 4 S 5 cage-like molecules, with a molecular packing closely resembling that found in the b-As 4 S 4 phase. Both As-As and As-S intramolecular distances are in the range usually observed for covalent bonds. The structural model confirms the chemical formula As 8 S 9 for alacranite, and accounts for differences in the unit-cell parameters of alacranite compared to those of the natural analogue of b-As 4 S 4 . This latter mineral, therefore, should receive a new name.