geojoek
Uknown granite, Barnstable, MA
Walks along a beach as a geologist can be both extremely interesting and confounding-- the bicep of Cape Cod, so to speak, is a re-worked glacial morraine, made up of sediment derived from bedrock to the north-- mostly that surrounding Boston. Pebbles, cobbles, and boulders of more resistant types of bedrock, namely, granite, are extremely common on these beaches. Whenever I walk a river or a beach, I can usually tell, with some accuracy, which bedrock unit a given pebble came from. Which is why it's extremely frustrating to me that I can't place this particular granite-- I don't believe I've seen it before. I've seen ones like it: nice pink microcline feldspar (rich in potassium!) is very, very common in the huge mass of granite underlying the eastern 1/3 of the state-- but to have them in nice euhedral crystals, with a little bit of alteration to what-looks-to-be-albitic feldspar along their rims? And the chalky white albitic (?) feldspar? The relative lack of quartz or dark mafic minerals? The pistachio green bits of epidote just hanging out as if they crytallized right out of the magma and weren't introduced later by hydrothermal alteration (although I have my doubts-- microcline doesn't get *this* pink-red without soaking in some juices). It looks a little bit like granites that are lumped into the catch-all unit of Dedham granite (used to describe pretty much all granite around Boston), but, well... I just don't know. The fun thing about geology, and science, is that there are always mysteries to solve. The bedrock geology of the southeastern 1/3 of Massachusetts is very poorly mapped-- many, many different granites all lumped together. I was hoping to eventually take a crack at these rocks amongst others, but, alas, no longer have that job-- it's unclear if anyone will be mapping that geology anytime soon-- it's something I've been wanting to see done, and I was hoping to be one of the people to do it.
Uknown granite, Barnstable, MA
Walks along a beach as a geologist can be both extremely interesting and confounding-- the bicep of Cape Cod, so to speak, is a re-worked glacial morraine, made up of sediment derived from bedrock to the north-- mostly that surrounding Boston. Pebbles, cobbles, and boulders of more resistant types of bedrock, namely, granite, are extremely common on these beaches. Whenever I walk a river or a beach, I can usually tell, with some accuracy, which bedrock unit a given pebble came from. Which is why it's extremely frustrating to me that I can't place this particular granite-- I don't believe I've seen it before. I've seen ones like it: nice pink microcline feldspar (rich in potassium!) is very, very common in the huge mass of granite underlying the eastern 1/3 of the state-- but to have them in nice euhedral crystals, with a little bit of alteration to what-looks-to-be-albitic feldspar along their rims? And the chalky white albitic (?) feldspar? The relative lack of quartz or dark mafic minerals? The pistachio green bits of epidote just hanging out as if they crytallized right out of the magma and weren't introduced later by hydrothermal alteration (although I have my doubts-- microcline doesn't get *this* pink-red without soaking in some juices). It looks a little bit like granites that are lumped into the catch-all unit of Dedham granite (used to describe pretty much all granite around Boston), but, well... I just don't know. The fun thing about geology, and science, is that there are always mysteries to solve. The bedrock geology of the southeastern 1/3 of Massachusetts is very poorly mapped-- many, many different granites all lumped together. I was hoping to eventually take a crack at these rocks amongst others, but, alas, no longer have that job-- it's unclear if anyone will be mapping that geology anytime soon-- it's something I've been wanting to see done, and I was hoping to be one of the people to do it.