Mg-vermiculite heated in air at 700 degrees C for more than 24 h gives a non-swelling new phase; a biopyribole. It is composed of two phases; an enstatite in epitaxy on the (010) plane of a phyllosilicate. The phyllosilicate has a semi-random layer stacking. The (h01) (super *) plane presents only discrete reflections, therefore the x0z projection can be obtained by classical two-dimensional Fourier analysis. The other rows of the reciprocal lattice are more or less diffuse in the c (super *) direction. The disorder is created by a random distribution of three translations between the layers. The structural relationship between the phyllosilicate and the enstatite phases accounts for the non-swelling behavior of the phyllosilicate.