Rocks in The Soil
Certain parent materials also contribute to soil acidification. Granites and their allied igneous rocks are called "acidic" because they have a lot of free quartz, which produces silicic acid on weathering. Also, they have relatively low amounts of calcium and magnesium. Some sedimentary rocks such as shale and coal are rich in sulfides, which, when hydrated and oxidized, produce sulfuric acid which is much stronger than silicic acid. Many coal spoils are too acidic to support vigorous plant growth, and coal gives off strong precursors to acid rain when it is burned. Marine clays are also sulfide-rich in many cases, and such clays become very acidic if they are drained to an oxidizing state.
Read more about this topic: Soil Acidification
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—Leo Robin (1900–1984)
“Green, green is El Aghir. It has a railway station,
And the wealth of its soil has borne many another fruit:
A mairie, a school and an elegant Salle de Fetes.
Such blessings, as I remarked, in effect, to the waiter,
Are added unto them that have plenty of water.”
—Norman Cameron (b. 1905)