Blue Quartz - (metamorphic rock)
Blue quartz from the Blue Ridge Mountains is valued as a decorative stone and for jewelry. Blue quartz is found in the older basement rocks of the Blue Ridge Province. Probable age, around Grenville time; Middle Proterozoic (900 – 1600 Ma).
Most blue quartz in Virginia is in the Blue Ridge Complex lying east of the Blue Ridge Mountains. The complex extends from Loudoun County in the north to Grayson County in the south. A few occur- rences of blue quartz have been reported from the Virginia Piedmont. Most of the blue quartz in Virginia is from metamorphosed magmatic rocks of the Blue Ridge Complex.
The blue quartz found in Virginia exhibits most of the physical properties of colorless quartz. It has a hardness of 7, displays conchoidal fracture, a white streak and it is infusible before the blowpipe. When heated it retains its color, unlike some smoky or amethystine varieties. The specific gravity of blue quartz is 2.65 or higher depending on the kind and amount of included material. Inclusion-free blue quartz tends to have a lower specific gravity than specimens containing inclusions. The uniqueness of blue quartz is due to properties that are uncharacteristic in ordinary quartz, opal- escence, chatoyancy, and asterism. In addition, all blue quartz specimens are highly fractured and contain inclusions of rutile or other minerals. OPALESCENCE AND CHATOYANCY A striking characteristic of blue quartz is its opalescent, or waxy, luster. This waxy to greasy appearance is seen in all blue quartz. Light blue specimens tend to be more opalescent than darker specimens.
Division of Geology and Mineral Resources - article
PFD file from DGMR with article on blue quartz https://www.dmme.virginia.gov/dgmr/pdf/vamin/VAMIN_VOL27_NO02.PDF