A direct in-situ visualization of montmorillonite gels at 50 gn has been obtained for the first time, using silicon fluorescence yield imaging at the ESRF ID21 X-ray microscopy line. An unexpected superstructure formed by alternating clay-rich and clay-poor domains was evidenced with mesoscopic orientational order. The order and size of the oriented entities extends over distances at least 2 orders of magnitude larger than the dimensions of individual clay platelets. Such long-range organization must certainly be considered for assessing the formation mechanisms and properties of gels in systems of charged colloidal platelets.