Rodingite

Rodingites are metasomatic rocks that are typically calcium-rich and formed by metasomatism of mafic or ultramafic rocks in serpentinites or other calcium-rich, high-pH environments. This metasomatism, called rodingitization, involves the introduction of calcium and depletion of silicon and alkali elements.

Formation:

The process of rodingitization is commonly associated with serpentinization, a process where ultramafic rocks such as peridotite react with water, altering their mineralogy and releasing significant amounts of calcium. This calcium-rich fluid then migrates through surrounding rocks, altering their composition. The exact mechanisms of rodingitization are complex and can involve various fluid pathways and chemical reactions. The protolith for a rodingite can be a variety of rock types, including basalt, gabbro, or even sedimentary rocks.

Mineralogy:

Rodingites are characterized by a specific mineral assemblage, often dominated by calcium-rich minerals. Common minerals found in rodingites include:

• Grossular garnet: A calcium-aluminum garnet.
• Hydrogrossular garnet: A hydrated form of grossular.
• Vesuvianite: A complex calcium aluminum silicate.
• Diopside: A calcium magnesium pyroxene.
• Clinozoisite/Epidote: Calcium aluminum epidote group minerals.
• Prehnite: A calcium aluminum silicate.
• Calcite: Calcium carbonate, present as veins or alteration product.

The specific mineral assemblage of a rodingite depends on the composition of the protolith and the composition and temperature of the metasomatizing fluid.

Occurrence:

Rodingites are commonly found in association with ophiolites, which are sections of oceanic crust that have been uplifted and exposed on land. They are also found in association with serpentinized ultramafic rocks in other geological settings.

Significance:

Rodingites are important because they provide insights into fluid-rock interactions and metasomatic processes in the Earth's crust. They can also be indicators of specific geological environments, such as subduction zones and areas of serpentinization. Furthermore, the mineralogy of rodingites can sometimes host economically valuable minerals, such as jade or garnet.