A new compound of the (K,Na)3Ca8Si6[Si4O12]3 charoite substrate
As a result of experimental studies on the interaction between a charoite substrate and host lamprophyres of microcline-arfvedsonitic composition, a new (K,Na)<sub>3</sub>Ca<sub>8</sub>Si<sub>6</sub>[Si<sub>4</sub>O<sub>12</sub>]<sub>3</sub> compound has been obtained with a new type of radical Si<sub>2</sub>[Si<sub>4</sub>O<sub>12</sub>] found in its crystalline structure <i>а</i> = 15.2613 (3) Å, I2/<sub>1</sub>3, <i>Z</i> = 4. The chain-shaped Ca-octahedra connected through common faces encircle a radical and close in a K-octagon. In contrast to charoite with banded-tube radicals, an isometrically-island silicon radical is identified.