Soil is what sediment turns into as a result of subaerial weathering (i.e. being rained on repeatedly, and the chemical processes that go along with that) plus having stuff growing in it.
Volcanoes erupt
volcanic ash, which is indeed turned into soil by these processes. Other sediments are produced by weathering and erosion, and then transported and deposited by water, wind, or glaciers. Pretty much any sediment once deposited can turn into soil given rain and enough time.
P.S: I wrote a short article about soils and paleosols (fossil soils)
here.
P.P.S: Welcome to the forums.
Edited by Dr Adequate, : No reason given.
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