David GraylessFeb 9
The geology of the #NorwegianSea began to form 60 million years ago in the early #Cenozoic, as rifting led to the eruption of #mafic oceanic crust, separating #Scandinavia and #Greenland. Together with the #NorthSea the Norwegian Sea has become highly researched since the 1960s with the discovery of oil and natural gas in thick offshore sediments on top of the #NorwegianContinentalShelf.
David GraylessOct 4
A pegmatite is an #igneousRock showing a very coarse #texture, with large interlocking #crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of #quartz, #feldspar, and #mica, having a similar #silicic composition to #granite. However, rarer #intermediateComposition and #mafic pegmatites are known. Many of the world's largest crystals are found within pegmatites. These include crystals of #microcline, quartz, mica, #spodumene.
Chris WhiteSep 29, 2023

#Mafic enclave (?) in Rattlesnake Hill #Granite, #Massachusetts

This Devonian granite intrudes #Proterozoic Dedham Granite south of #Boston. It is younger than the nearby Blue Hill Granite Porphyry. The triangular area is rich in large crystals, possibly hornblende. The blue crystals at lower left may be #riebeckite, another amphibole. Riebeckite gives Quincy Granite and the #BlueHills Range their distinctive color. All on Avalon terrane, out of Gondwana. Acadian Orogeny was Devonian. My #photo

Chris WhiteFeb 1, 2023

Where is Babel Rock?

The #USGS #BlueHills #quad #bedrock map and a #Quincy #Massachusetts #historical #map show Babel Rock overlooks a pond from just north of a bend in #Wampatuck Rd. I have been on that rock, and it's #diabase, a #mafic #intrusion into the Quincy #pluton. But the USGS #topographic quad & derivatives e.g. #GoogleEarth show it adjacent to the #BunkerHill #quarry (source of the #granite for the monument in #Boston).

Should a correction be proposed to USGS? Advice welcomed.