Date: the diamond dates to c. 1920s. The pendant is more difficult, but it its method of construction and lack of plating suggests that it, too, is quite old. Likely no later than the 1950s. The chain is impossible to date.
Pendent: solid 14K white gold; approx. 4.75 mm
Chain: 16 inches; solid 14K white gold; .60 mm thickness
Diamond: .60 carat (est) Old European Cut diamond; K-L color (a soft yellow with a touch of silvery-green); VS2 clarity