Phyllite

I spent a good deal of time exploring the stone steps and so did many of my readers.  For this reason, I am re-posting the photo before continuing my journey.  It will all fit together.

[Those of you who have not read yesterday’s post will find it helpful with this post. Click to read.]

Originally posted in A New World

The colorful stones are part of what is referred to as The Casco Bay Group.  Specifically, The Jewell Formation with the description as being  Rusty and non-rusty weathering mica-rich schist and phyllite of the Ordovician period some 445-475 million years ago.  Source:  https://www1.maine.gov/dacf/mgs/pubs/online/bedrock/85-87.pdf

The Ordovician period was a busy time for geological events.  I’ll still to the “rocks” here.  The source article states the following, “Partial closing of Iapetus Ocean brings about collision of island arc of western New Hampshire with North America resulting in the Taconic Orogeny.  Collision of Casco Bay island arc with AvaIonia results in deformation of rocks of Casco Bay Group.  Deposition of formations of the Casco Bay Group; volcanism associated with ocean 485 lithosphere builds island arc.”

What I’m most interested in is the phyllite as it is the chief component of the rock steps and of the southwestern portion of Jewell Island.  “Phyllite is between slate and schist in the spectrum of metamorphic rocks.  Phyllite has flat or crinkled cleavage faces and shiny colors, and schist has intricately wavy cleavage and glittering colors.”  Phyllite generally is in the pelitic series—rocks that are derived from clay sediments—but sometimes other rock types can take on the characteristics of phyllite too. That is, phyllite is a textural rock type, not a compositional one. The sheen of phyllite is from microscopic grains of mica, graphite, chlorite and similar minerals that form under moderate pressure.” Source:  http://geology.about.com/od/more_metrocks/ig/phyllite.-CN2/

…  I turn toward the sea and find it as magnetic to my senses as it has been since we first met.  I am greeted with kaleidoscopic variables every time I visit, with each glance or blink of the eye. This space, where my feet are planted is as ever changing and enchanting as the previous moment. However, I feel compelled to let it be for now and take advantage of the low tide.  I wish to investigate the features of the southwest end of Jewell Island.

My feet sink into finely ground stones with each step, adding a personal contribution toward geological history.  The high bank has a distinct rusty colored belt.  This feature adds pyritiferous shale to the phyllite picture.  Pyrite is all sparkles and fun to look at.  But when these crystals are exposed to the elements, they disintegrate.
“Metamorphism can cause the pyrites to grow as quite large crystals which are hard and shiny when the slate is freshly split. But beware! Pyrites are notoriously unstable when exposed to air and rain and will soon rot away to a rusty stain, leaving a hole. Some pyritic slates will rot away completely.
Source: http://www.naturalstonespecialist.com/information/slate.php

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This “rotting away” is clearly demonstrated at the bank by the stone steps.

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There is significant erosion due to the oxidation of pyrite as well as the sedimentary nature of phyllite.

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About Just Jude

I grew up on a small farm in Michigan but have always felt the urge to wander and began doing so as a teenager. Since that time, I've hiked, biked and paddled in every season; not for sport, but for the journey.

Posted on March 19, 2015, in Casco Bay, Geology, Jewell Island, Maine, Maine Coast, Rocks, Solo Journeys, Twenty One Days at Sea and tagged , , , , . Bookmark the permalink. 4 Comments.

  1. Very interesting!
    We have Ordovician fossils in our area that I collect. (Silurian and Pennsylvanian too!) 🙂

    Liked by 1 person

  2. Now that is beautiful scenery

    Liked by 1 person

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