The cat's eye effect is called chatoyancy. It's caused by tiny parallel inclusions in the chrysoberyl crystal that reflect light in a concentrated band. As the stone moves, the bright line appears to travel across the surface, opening and closing like the pupil of a cat. Cutting the stones into domed cabochons maximizes this eerie effect. They're great alongside clear, faceted diamonds.
MATERIALS: 18k gold (marked), 2 4.5mm cat's eye chrysoberyl cabochons, 3 old European cut diamonds (2 approx. .20ct , 1 approx. .25ct)
AGE: c. 1880
CONDITION: Very good - one tiny nibble on the girdle of one side diamond
SIZE: 7, can be resized; 5.7mm head, 2.4mm shank