Type II twinning in devitrite, Na2Ca3Si6O16

Abstract

Nanometre-scale twins found in the triclinic crystalline phase devitrite, Na2Ca3Si6O16, are shown to exhibit the relatively rare form of twinning, Type II twinning, in which the crystal structure of one of the parts is related to the crystal structure of the other by a rotation of 180° about η 1 = [1 0 0]. Although formally, the twin plane K 1 is irrational, it is in essence (0 1 0).