The structure of nekoite, Ca₃Si₆O₁₅·7H₂O, a new type of sheet silicate Available to Purchase

Nekoite, Ca₃Si₆O₁₅ · 7 H₂O, is a new type of sheet silicate. The sample studied, from Caxias do Sul, Rio Grande do Sul, Brazil, is triclinic, space group P1, with a = 7.588, b = 9.793, c = 7.339Å, α = 111.77, β = 103.50, γ = 86.53°; Z = 1. The structure was solved through a combination of direct methods and the Patterson synthesis, and refined to a final R factor of 6.8 percent. The crystal structure consists of tetrahedral sheets interlayered with octahedral chains. The tetrahedral Si₆O₁₅ sheets are obtained by interconnecting a “Dreierkette” so as to form alternating bands of 5- and 8-membered rings. Ca-octahedral chains, which crosslink the tetrahedral sheets, are formed by a double strand of octahedra, of which three out of four are occupied and the fourth is empty. Water molecules occupy the empty spaces between these chains. The balance of the electrostatic valences suggests that only oxygen atoms occupy the vertices of the tetrahedral sheet, while only water molecules occur outside the tetrahedral sheet.