The petrology field trip got me thinking...just what was so interesting around Lanes Cove. I posted a question on a local forum and someone posted a USGS (US Geological Survey) bedrock map of Cape Ann. Just south of Lanes Cove (where the field trippers were looking) were a couple of diamonds. I asked what they represented and the reponse was "Hornblende diorite porphyry inclusions - Predominantly Salem Gabbro-diorite porphyry characterized by large (up to 10 cm (4 in.) long) white-weathering, red-purple labradorite phenocrysts"
Now, I wouldn't know a labradorite phenocryst if it bit me on the a**. This morning was the first time I could get out there during the daylight, so I took a few pictures and e-mailed one off to Prof. John Brady
, Geology Dept. Chair of Smith College
in Northampton, Mass. He was kind enough to inform me that my photo was a "pegmatite dike
" with bluish quartz crystals.
Prof. Brady was also nice enough to send me a picture
of the diorite porphyry inclusions that were taken on Sunday.
I guess I'll have to get out there and see if I can find those phenocrysts