Ghost-Rock Karstification is a two stage process where the soluble part is removed first by dissolution and at some point the remaining, weakened "ghost" rock is removed by erosion. It works with rocks which are not suitable for classical karstification, as long as they have a soluble component and pore space.
Ghost-Rock Karstification is a two stage process that differs in many respects from the traditional single-stage process of karstification.
The first stage is chemical dissolution and removal of the soluble parts of the rock. It requires only low hydrodynamic energy, which means water filled cracks with slowly moving water, and creates a ghost-rock, filled with residual alterite. In other words the insoluble part of the rock remain in the structure in which they occurred in rock. The soluble part is dissolved, but may have left some small loose insoluble part, typically clay minerals, iron oxide or quartz called residual. And while not dissolved, it may nevertheless have been changed by the chemical processes.
The second stage is characterised by mechanical erosion of the undissolved parts. This requires high hydrodynamic energy, in other words a flowing cave river, which transports the loose sediment away. The structure of the residual is typically fragile, and easily destroyed by the flowing water. The rest is plain erosion.
The name "ghost" comes from the properties of the rock after the first phase. Due to the dissolution of a part of the rock, it has a large pore space, is very light and very soft. In other words, it is only the ghost of the rock, looks the same as before but is only a shadow.
Ghost-Rock Karstification was first described in the Belgian Ardennes, so the original name is the French version karst fantômique.