Excavations within this quarry in the Medicine Lake Volcano area of California reveal vertical veins of obsidian & globule vesicles of cristobalite, an uncommon form of silicon dioxide.  This is a well-known collection locale for the mineral; a variety of obsidian known as snowflake obsidian is also comprised of cristobalite.  In this view, each vertical line of obsidian is roughly 1-3 inches thick.  Some of the larger cristobalite pockets also contain millimeter-size crystals of fayalite, appearing copper in color.