File:Madocite (tourmaline-pyrite metamorphite), Madoc Ontario.jpg

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“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.
Date
Source Madocite (tourmaline-pyrite metamorphite) (Precambrian; Canada Talc Limited Mine, Madoc, south-central Hasting County, se Ontario, se Canada)
Author James St. John

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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/14874133400. It was reviewed on 31 August 2014 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0.

31 August 2014

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current21:18, 31 August 2014Thumbnail for version as of 21:18, 31 August 20143,008 × 2,000 (2.37 MB)Tillman (talk | contribs)Transferred from Flickr via Flickr2commons

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