12 x 18mm. The bail and setting is sterling silver with a touch of rhodium which helps prevent tarnish. This pendant is made with AAA top quality Herkimer Diamonds. Herkimer Diamonds are quartz formations which because of their brilliance and diamond shape have been given the name. Mined only in Herkimer, NY. Herkimer diamonds help release energy blockages and also help enhance dream recall. Really nice!