Thursday, April 06, 2006

More on Petrology

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.

Hornblende diorite porphyry inclusions

Prof. Brady was also nice enough to send me a picture of the diorite porphyry inclusions that were taken on Sunday.

pegmatite dike with bluish quartz crystals

I guess I'll have to get out there and see if I can find those phenocrysts.


  • Happy hunting, Stan.

    I took a couple of geology courses in college --- many years ago. It is fascinating stuff.

    If you ever find yourself in central Pennsylvania a trip to the Geology Museum at Penn State is worth the time.

    By Blogger Kathleen Valentine, at 9:50 AM  

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