|Is a Variety of||Chalcedony|
|Colors||Blue to blue-green.|
|Optics||o = 1.540; e = 1.553. Uniaxial (+).|
|Optic Sign||Uniaxial +|
Marketed as “Gem Silica” this relatively rare, blue to blue-green, opaque to near transparent material is the most expensive type of chalcedony. Found almost exclusively in Arizona its color is due to copper. Those who take the trouble to seek it out and are willing to pay the price are rewarded with a glorious color, (elsewhere found only in the soft gem Chrysocolla,) in a stone that has the durability and hardness of quartz.