A particularly staggering specimen of Brazilian Super Seven quartz* is sheathed in a setting of both yellow and white gold, making for a spectacular amulet.

18k yellow & palladium white gold 
Super Seven quartz, 31mm x 17mm (1 1/4" x 11/16")
1.5mm rolo chain is 18" long

"Super Seven" is a type of stone, typically quartz, that holds seven specific minerals: amethyst, clear quartz, smoky quartz, cacoxenite, rutile, goethite, and lepidocrosite. It is known for its often dramatic patterns & color gradation.