#felsic

2023-09-08

Interesting #boulders in a roughly stacked #seawall
The southern part of the spit separating #Plymouth Harbor from Plymouth Bay has a seawall along the outer shore, above Plymouth #LongBeach. Without knowing where they came from, interpreting the boulders is sketchy. BUT nice coarse crystals in intrusions into #felsic rocks, including big #quartz chunks (top right photo) and blades of #biotite (bottom right).
#Massachusetts #igneous #geology #intrusion #pegmatite #NewEngland #dike #rock #beach

Plymouth bay is on the Massachusetts coast between Boston and Cape Cod. The spit protecting Plymouth Harbor (lower right) is about 4 km long.A vein bearing large grayish quartz crystals in a fine grained ground mass intrudes into felsic rock, sunglasses for scale.A view southward along Plymouth Long Beach, with the varied boulders of the seawall at right.A plagioclase-rich vein with large blade-shaped biotite crystals, with an example being indicated by Karen’s finger.

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