Diabase is often considered to be relatively erosion resistant. We can generally find diabase dikes cross-cutting various strata through the geologic landscape, wherein, the diabase dike or sill is rather intact as a structure while the surrounding strata have eroded around it.

Of course, differential weathering and erosion depend on the relative susceptibility among those rocks which are next to each other, but if you take into consideration the Goldich Dissolution Series, shouldn't diabase and other basalt-like bodies be easily eroded? Basalts and diabase have calcium plagioclase as a major mineral component.

I could see how shales could weather and erode much more quickly but it seems unlikely that a limestone in an arid environment or a mature quartz arenite sandstone ever would do so.


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Diabase is indeed relatively erosion resistant. One of the reasons is grain size.

Consider the two other chemical equivalent of diabase: gabbro (coarse-grained) and basalt (glassy and fine-grained), which should potentially be similarly erosion resistant. This is not the case. Both gabbro and basalt erode very easily.

Coarse-grained rocks, in general, erode easily. The large grain size means it is relatively easy to dislodge individual grains out of the rock. You don't need a lot of water, for instance, to percolate between the not-many grain boundaries and release them. To make it worse, gabbros are full of minerals that are easily erodable such as plagioclase and olivine.

On the other hand, basalts also tend to weather easily. Having cooled fast, they are usually glassy which tends to crack during cooling. Glass is general is less resistant to chemical alteration than minerals, under similar conditions. Basalts also contain gas bubbles, which cause weakness spots in which the rock can break, leading to preferred weathering.

Diabase is fine grained, and contains no glass. It does not suffer from these two conditions. It is composed of very fine interlocking crystals that are very hard to dislodge, and is not penetrable by fluids.

That said, remember that it is all relative. A diabase will still weather faster than even the worst type of granite.


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