The color was deep to sky blue, and seemed to changed in hue as I tilted it. Like most blue quartz, it was not gemmy and was cross-cut by many fractures stained with iron oxides.
Blue quartz occurs at many localities.
One famous localities is in Llano County Texas where it is found as small doubly terminated crystals in a rhyolitic porphyry called, informally, llanoite. The crystals weather loose and can be collected easily. Slabs of this rock studded with blue crystals are cut and polished. Blue quartz is found in Wisconsin, most notably in a diorite exposed by the Dairyland Power Dam near Tony. The cause of the blue color is reasonably well known.