Continuing along the crest towards the north, we again encounter some feldspar-rich felsic gneisses of the Serra di Pigno unit. In contrast to the last location, here we can observe a light-greenish mineral called jadeite. In fact, this is not pure jadeite (nor gem jade), but its composition is very close. This mineral indicates metamorphism at high-pressure and low- to intermediate-temperature, hence at conditions typically found within subduction zones (i.e., material brought at great depth yet maintained relatively cold). In the same rock, we also find another mineral, albite (Na-rich feldspar), which partly replaces jadeite and is formed by the breakdown of jadeite at lower pressure conditions, during retrograde metamorphism. This evolution accompanied the return of the rock towards the earth's surface, in other words, its exhumation. This metamorphic evolution overall indicates that this fragment of continental crust was subducted at ~30-40 km depth and then returned to the surface.
