July 10, 2007
This blue quartz megacrystal is located in the pegmatites of the Cape Ann granite at Andrew’s Point in Rockport, Massachusetts. The Cape Ann granite is an igneous rock formation that's part of the Avalon terrane in southeastern New England. This terrane collided with Laurentia (old North America) in the late Ordovician through the Silurian periods, during the Taconic Orogeny (around 440 million years ago). The Cape Ann granite may have formed from the dry melting of lower crustal rocks in response to heat added by mafic melts that underplate the crust at the mantle-crust interface.
Blue quartz gets its color from Rayleigh scattering of sunlight as a result of inclusions in the crystal structure. These inclusions could be a variety of minerals including: ilmenite, rutile, tourmaline, crocidolite, magnesioriebeckite, or zoisite (maybe others).
Photograph taken on March 11, 2007 during a spring field trip sponsored by the Geological Society of America (northeastern sectional meeting) and was led by Rudolph Hon, J. Christopher Hepburn and Jo Laird.