Bull. Minéral. (1984), 107, 499-507

Crystal structure and Al/Si-ordering of a synthetic nepheline

Structure cristalline et ordre Al/Si dans une néphéline synthétique.

Introduction

Nepheline is a tectosilicate of both natural and synthetic origin and approximate composition

(□,K,Na)Na3[(Al,Si)204]4. Its average crystal structure is known (Hahn & Buerger, 1955) and

consists of a framework [AlSi04]~ with tridymite topology, where 3/4 of the cavities are adapted to the small size of the sodium ions, whereas the remaining 1/4 is mainly occupied by po¬ tassium ions and retains a large and open confi¬ guration (Figure 2).