Abstract
The crystal structure of rankinite has been determined by Patterson and direct methods and refined to R=11.6%, using a crystal from Fuka, Bitchu-cho, Japan: P21⁄a, a 10.60(2), b 8.92(2), c 7.89(2)Å, β 119.6(1)°, Z=4 Ca3Si2O7. There are in the structure arrays of Si2O7 groups parallel to the c axis, and the groups are linked together by Ca’s each having seven near oxygen atoms: the Ca–O bond length in the structure is in the range from 2.25 to 2.90 Å. Si–O is from 1.52 to 1.65 Å. The structural relationships between rankinite (Ca3Si2O7) and kilchoanite [Ca6(SiO4)(Si3O10)] are described briefly.
