Madocite (tourmaline-pyrite metamorphite) (Precambrian; Canada Talc Limited Mine, Madoc, south-central Hasting County, se Ontario, se Canada)

License: Creative Commons - Attribution
Author: James St. John
“Madocite” (field of view ~2.7 cm across) from the Precambrian of Ontario. -------------- Here’s a rock from Ontario having a mineral combination you don’t see very often. This sample is from a metamorphosed mafic dike that intrudes tremolite-talc schists hosted in dolomitic marble. The metamorphism has converted the original mafic igneous minerals into a mixture dominated by tourmaline (black) and pyrite (brassy gold). Some of the small bright white patches are talc. Tourmaline-pyrite metamorphic rocks lack a formal name, so the term “madocite” has been used by some geologists. Published mineral analysis indicates that “madocite” contains tourmaline, pyrite, tremolite, and some phlogopite mica. Age of metamorphism: probably ~1.24 billion years, during the Mesoproterozoic. Subsequent metamorphism occurred at ~1.1 billion years, during assembly of the Rodinia supercontinent. Initial metamorphic agent: probably emplacement of the nearby Deloro Granite. Locality: Canada Talc Limited mine at Madoc, south-central Hastings County, southeastern Ontario, southeastern Canada. ----------- Most info. from: Dunn (1998) - Formation of dolomite-hosted massive talc at Madoc, Ontario. Geological Society of America Abstracts with Programs 30(7): 229-230.


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