By means of transmission electron microscopy (TEM) and the gold decoration technique, the surface microtopography of rectorite (allevardite) crystals collected from Allevard, France was investigated. On the crystal surfaces, gold decoration successfully revealed growth steps of approximately 20Aa in height. Only closed polygonal steps 20Aa high occur on the 001 surface of a thick platy crystal, although spiral growth patterns were not observed. Thick platy particles were easily split into thinner plates 20Aa thick in distilled water by means of ultrasonic vibration. No step patterns were observed on the surfaces of these thin plates which correspond to the cleavage plane. The growth of this rectorite, therefore, seems to be controlled by a layer nucleation mechanism.

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