U.S. Geological Survey Open-File Report 03-221
A Pictorial Survey of the Bedrock Beneath Western Cape Cod, Massachusetts

Thin Section of 95MW0212

Photomicrograph of Mylonite

$A large K-feldspar porphyroclast in a mylonite of syenitic composition (no quartz) shows evidence of movement on a fine fracture. Note the growth of finer grains of plagioclase and microcrystalline muscovite in the “shadows” of the faulted porphyroclast. K-feldspar has been stained green, and Na-rich string perthite appears gray.$

A large K-feldspar porphyroclast in a mylonite of syenitic composition (no quartz; 95MW0212) shows evidence of movement on a fine fracture. Note the growth of finer grains of plagioclase and microcrystalline muscovite in the “shadows” of the faulted porphyroclast. K-feldspar has been stained green, and Na-rich string perthite appears gray. Click here for a zip file with full resolution image.

kfs: K-feldspar
ms: muscovite
pl: plagioclase

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