Volcanic rock of Mount Etna can be transformed into Limonite, which is called like that because of its yellow brownish color. The Limonite is mainly produced by the oxidation of iron containing lava rocks by weathering, facilitated by splitting and pulverizing of the rock because of the penetration of the roots of vegetation enabling oxygen and humidity to enter.
This process takes hundreds of years and is accelerated from the beginning by the settlement of lichens on the bare rock, its roots scratching the surface. Lichens are one of the pioneer species one Mount Etna.
The (chemical) weathering process, makes the minerals in the lava rock to oxidize, thus changing the mineral composition. When minerals in rock oxidize they become less resistant to weathering, which further promotes the process. The result of this process is the creation a very fertile soil with a clay-like look, which holds a pallet of useful minerals, on which finally trees and other more sensitive and endemic vegetation can grow.
Not yet affected volcanic rock from Etna
Limonite from Etna
With thanks to Sebastiano Mirici, Mount Etna tour guide.