Abstract
Miargyrite is the low-temperature monoclinic derivative of a high-temperature cubic galena/halite structure. The essential features of its crystal structure (Knowles, 1959) were confirmed, but the details of the bonding changed [new space group C121; a 12.824(1), b 4.4060(3), c 13.193(1) Aa, beta 98.567(6) degrees ]. The octahedral connectivity of galena/halite is severely distorted: Ag(1), 2S each at 2.53, 2.66 & 3.39 Aa; Ag(2), 2 each at 2.54, 2.62 and 3.44; Ag(3), 2.38, 2.40, 3.05, 3.05, 3.53, 3.58; Sb(1), 2.45, 2.50, 2.51, 3.22, 3.28, 3.41; Sb(2), 2.45, 2.50, 2.51, 3.22, 3.28, 3.41. The short distances define the following coordinations: very distorted tetrahedral Ag(1) and (2); near-linear Ag(3) at 178.9(2) degrees ; trigonal-pyramidal Sb(1) and (2) at 92.0, 93.6 and 96.8 degrees . The ten shortest S-S distances range from 3.61 to 3.77 Aa.
