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

Thin Section of 69MW1603

Photomicrograph of Orthogneiss

K-feldspar porphyroclast in a fine-grained felsic gneiss showing tartan twinning. Note the relatively straight grain boundaries in matrix K-feldspar, indicating recrystallization. Biotite, aligned in the foliation, wraps the porphyroclast of K-feldspar.

K-feldspar porphyroclast in a fine-grained felsic gneiss (69MW1603) showing tartan twinning. Note the relatively straight grain boundaries in matrix K-feldspar, indicating recrystallization. Biotite, aligned in the foliation, wraps the porphyroclast of K-feldspar. Click here for a zip file with full resolution image.

bt: biotite
kfs: K-feldspar

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