Rodingite

Rodingites are Calc-silicate rocks associated with serpentinites, the a name was given originally by Bell et.al (1911), to lime-rich, coarse- to fine-grained, altered gabbros, composed primarily of grossular and prehnite in the vicinity of the Roding River in the Dun Mountain ultramafic complex, New Zealand.

Rodingites are fine grained, dense, withe, green or pink colored rocks rich in Calcium-aluminum-silicate minerals (Grossular, Phrenite, Wollastonite, Vesuvianite, Diopside, Tremolite, Chlorite, Spinel, Calcite, Quartz). They are locally developed along serpentinite-country rock contact or, more commonly, as dike, sills, pods or boudin completely enclosed by serpentinite. Rodingites are frequently found at the contacts between serpentinites and mafic or felsic intrusive bodies, also commonly occur at the contacts between serpentinized peridotites and country rocks of diverse origin. In all cases, these calc-silicate rocks are metasomatic products of the alteration of the various rock types in contact with serpentinite, and, in some cases, of the serpentinite itself. mass transfer, during metasomatic processes, is believed to be of the infiltration type and is due to circulation, during serpentinization, of an aqueous fluid of high pH and high Ca2+ and OH- contents.

In Italy those kind of rocks are better known as Granatite (an old name) and generally are associated with the serpentinized ultramafic rocks of the Western Italian Alps. For the most part they are lenticular and are characterized by the presence of lithoclases with very beautiful crystals of garnet, sometimes in paragenesis with a few other minerals. Similar lithotypes , much more rare, can be formed with a preponderance of vesuvianite , epidote or diopside. Their formation was , in the past , assigned to contact metamorphic processes of carbonate rocks tectonically included in the ultramafics or to the transformation of original gabbro bodies.

Rodingite embedded in serpentinite. Mnt. Avic (Aosta). Italy

Rodingite. From C. Van Hove

Bibliography

• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori.
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• Anthony R. Phillpotts & Jay J. Ague: Principles of igneous and metamorphic petrology. Cambridge editore.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005)

Photo
Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)
Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)
Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink), magnetite (black) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)
Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)
Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)
Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)	Garnet (pink) and chlorite (pale-green) in a rodingite. PPL image, 2x (Field of view = 7mm)