『Abstract
　The behaviour of gypsum {010} cleavage faces, both (010)and (010)（1の頭に-）, in undersaturated conditions is studied at real time to probe the mineral dissolution process. The observations in surface topographic change and step motion made by in situ fluid cell atomic force microscopy show that: (i) the only type of each pits on the cleavage faces is that embraced by the [100] and [001] steps, disagreeing with previous reports that suggested the involvement of the [101] direction; (ii) compared to calcite, the anisotropy in step velocity is much more pronounced, presumably due to the more significant difference in atomic structure between the [100] and [001] steps on gypsum relative to that between the <441（最初の4の頭に-）>+ and <441（最初の4の頭に-）>- on calcite; (iii) the step kinetic behavior follows the prediction of the transition state theory; (iv) the dissolution process on gypsum {010} faces is not characterized by the formation of deep etch pits, even in which the increase in pit depth is out-paced by that in the lateral dimension.

Keywords: Etch pits; Gypsum; AFM; Step kinetics; Anisotropy; Transition state theory』

1. Introduction
2. Materials and methods
　2.1. Sample and solution preparation
　2.2. Imaging by fluid contact AFM
　2.3. Step speed measurement
3. Experimental observations and discussion
　3.1. Crystallographic orientation of the etch pits
　3.2. Anisotropy of step speed
　3.3. Step kinetics and Gibbs free energy
　3.4. Depth of etch pits
4. Concluding remark
Acknowledgements
References