English: (cut & polished surface; ~7.7 centimeters across at its widest)

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Rodingite is a type of metasomatic rock. "Metasomatism" refers to metamorphism principally by chemical change (other causative agents of metamorphism are heat and pressure). Rodingite forms when mafic igneous rocks (such as gabbros) are chemically altered by serpentinization of a nearby mass of peridotite. The chemical change is principally by the addition of calcium (Ca+2), which gets expelled from serpentinized peridotite bodies. Rodingite mineralogy is variable, but typically includes calcic pyroxene and various types of garnet, such as grossular and hydrogrossular.

The rodingite seen here is from the Canari area of Corsica. A large chrysotile asbestos mine operated in the area from the late 1940s to the mid-1960s. Asbestos occurs in a serpentinized peridotite body, with surrounding units including greenschists, metamorphosed gabbros, and metamorphosed pyroxenites. Minerals reported in the rodingites around the serpentinite mass include grossular garnet, hessonite garnet, andradite garnet, chromiferous garnet, diopside pyroxene, vesuvianite, calcite, wollastonite, epidote, and chlorite (Goujou, 1998).

The rocks in this area of Corsica are part of an ophiolite complex. Ophiolites are sections of oceanic lithosphere (basaltic / gabbroic crustal rocks + ultramafic upper mantle rocks) that have been metamorphosed and plastered onto the edges of continental lithosphere, usually by obduction (the opposite of subduction). The protoliths of the Corsica ophiolite rocks are Jurassic-aged oceanic lithospheric rocks and overlying sediments. Tectonic rifting and the formation of mafic oceanic lithosphere started at about 160 million years ago, during the Middle to Late Jurassic. Metamorphism of these rocks occurred during the late Mesozoic to Tertiary. What was originally mantle peridotite is now asbestos-bearing serpentinite. Rodingite formation in the area also dates to the late Mesozoic to Tertiary.

Geologic unit: Schistes Lustres Complex (Jurassic-aged protolith & Cretaceous- to Tertiary-aged metamorphism)

Locality: unrecorded / undisclosed site at or near the town of Canari / at or near the Canari Mine, western side of Cape Corsica, northeastern Corsica (Alpine Corsica), Mediterranea Sea

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Info. mostly synthesized from:

Goujou (1998) - Minéralogie des rodingites de la mine de Canari, Corse, France. Le Règne Minéral 20: 11-24.

Robertson (1999) - British Gelogical Survey Rock Classificaiton Scheme, Volume 2, Classification of Metamorphic Rocks. 24 pp.

Marroni & Pandolfi (2003) - Deformation history of the ophiolite sequence from the Balagne Nappe, northern Corsica: insights in the tectonic evolution of Alpine Corsica. Geological Journal 38: 67-83.

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Info. at: en.wikipedia.org/wiki/Rodingite and

en.wikipedia.org/wiki/Metasomatism