I gave an answer to the orientation and dip of planar architectural elements in alternating sedimentary sequences which can also be translated into fluid migration and hydrogeology as a function of rock strenght on a macroscopic to microscopic scale

If you consider folded and foliated/faulted sequences of alternating soft/fine-grained and hard/coarse-grained rocks you will recognize fanning and refraction in the hinge zone and an increase of the spacing of the axial plane foliation towards the limbs of the fold with a wider spacing observed in hard rocks than in the soft rocks, even if they belong to the same structural plan of deformation. Such a planar architectural element is genetically related to the fold plane but it is not strictly parallel to it but dependent on the distance from the zone of the most intensive deformation. The other effect in psammopelitic rocks is a refraction (similar to optical processes as a beam penetrates material of different refractive indices) with a more or less right-angle penetration of the psammitic and an inclined penetration of the pelitic rocks. It is a function of different lithological features of the sediments and the proximity to the zone of high shear strain.

HGD

like in the Khast topography, the water-rock interaction is effective at the dissolution of the rocks and weakening their strength.

Harald G. Dill Thank you for your detailed answer.

If I understand well, it is not possible to have this ranking of rock strength on geological domains because it may depends on several other factors either macro and microscopic and the formation of the rock itself.

However, is a first order approximation possible between rocks characteristics ?

Is it possible to rank sedimentary, plutonic, volcanic and metamorphic rocks on a strength scale ? And potentially on their geologic age ?

Hi Amaury,

There is not a classification for your case but there is definitely a relationship between rocks' hardness and strength with hydrological interactions. The main process in this regard is water-rock interactions which is strong in soft rock types and the host rocks with high amount of cracks and interaction surface.

There are factors intrinsic to the rocks and to the recharge and reservoir conditions. If we can make a matrix of characteristics of rock types in sedimentary basin environments and in areas that have already undergone tectonothermal processes, comparatively, we can obtain a better understanding of the water circulation in each of these possible conditions. Two aspects are not enough. But we can mention a few - 1 types of aquifers by types of carrier rocks - 2 weathering conditions of these rocks - 3 conditions of the rheological consequences that these rocks were subjected to (micro fractures, faults, associated with each type of rock - 4 which conditions occur for water reserve in each type of rock 5 - soil depth relationships in each type of rock - 6 topographic spatial analysis of sources to understand where recharge levels occur - 7 - recharge as a function of stratigraphy and this in relation to topography, and many other aspects. At least these are all indications. Hardness and strength of rocks are two aspects among many others, just.