MADOCITE

 

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.

 

Madocite” (field of view ~2.7 cm across) from the Precambrian of Ontario.

 


 

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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