Wind and water erosion are least likely to affect igneous sills and cooled lava flows. Limestone, basalt and quartzite are also unlikely to undergo erosion or weathering, as are sandstone and chert. Soil and soft rocks such as clays erode very quickly without protection.
Non-erosive geological materials are present in sedimentary, metamorphic and igneous rock types. The greatest erosive force is water, while wind tends to pick up and move only the finest particles. The three main factors contributing to resistance to erosion and weathering are hardness, chemical reactivity, also called inertness, and cohesion. When these characteristics are factored together, they reveal the probability of a material to erode, with higher factors indicating greater resistance.