Et elle est recouverte de magnésium.. j'ai laver une petite partie mais on voit bien la croûte.. quont appel varnish rock.. ou desert varnish.. jai lu cela..
Desert varnish often obscures the identity of the underlying rock, and different rocks have varying abilities to accept and retain varnish. Limestones, for example, typically do not have varnish because they are too water-soluble and therefore do not provide a stable surface for varnish to form. Shiny, dense and black varnishes form on basalt, fine quartzites and metamorphosed shales due to these rocks' relatively high resistance to weathering.