Sunday, September 29, 2013

9 Stories from my Stone Pile

1. The Layers
The layers in this rock suggest that it accumulated over time as sediment piled up somewhere. In the case of this rock it most likely occurred at the bottom of an ocean.

2. The Metamorphosis 
The layered rock was exposed to intense heat and pressure. Though not hot enough to melt the rock the heat and pressure were sufficient to cause minerals to migrate through the solid rock toward one another. This migration fused microscopic clay particles into visible shards of mica pictured here.

3. The Mixing
The dark gray rock in the picture above has a composition similar to the rock above. When Africa collided with North America the magma that formed the white rock rose from below the ocean bottom. Hunks of ocean bottom floated in the molten rock like ice cubes as the liquid rock hardened into the light colored rock.

4. The Crystals 
As the light colored magma cooled, similar minerals were drawn toward one another. Because cooling happened deep underground minerals could move freely through the warm liquid. The pockets of quartz (clear), hornblende (black), and feldspar (white) grew larger and larger until they froze into solid crystals.

5. The Big Crystals 
As the mass of crystals from the picture above solidified, they may have shrunk or cracked leaving space for water and more magma to pulse through the spaces. The water allowed the crystals to grow even larger than regular granite, making a rock called pegmatite.

6. The Splitting

As we all know Pangaea was not a permanent fixture. When it split it was not a clean break. Many places in Maine cracked, creating fractures throughout the coastal region. These joints provided space for new rocks, like the black one above to get up close and personal with older rocks.

7. The Black Rock 
Earlier, I mentioned that the light colored magma came when Pangaea formed. Less dense granite tends to form when continents collide, while dark basalt, pictured above is a sign of splitting. As the two hunks of massive continent diverged, magma that formed through this black rock spilled through every crack it could find.  This dark rock is Pangaea's swan song. 

8. The Ice
Bedrock tends to break off at relatively sharp angles.  Streams tend to form rounded rocks.  These stones fall somewhere in the middle.  They have softened edges, but flat faces.  A mile of ice covered this spot several thousand years ago.  The glacier scraped every type of bedrock in Maine, plucking off chunks as it went.  The glacier broke away hard edges, and sanded off flat facets as rocks were dragged across the ground.

9.The Pile 
The glacier grabbed everything it could, from clay to boulders, and everything in between.  Farmers could plough through the small stuff, but these stones got in the way.  As the freeze-thaw cycle of Maine's weather brought stones to the surface, farmers fought back by flinging them to the edges of fields.  Here lie the remains of decades of farm labor and hundreds of millions of years of geologic history.

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