Cat's Eye Chrysoberyl

Cat's eye chrysoberyl is the chatoyant variety of chrysoberyl, a beryllium aluminum oxide (BeAl₂O₄), in which parallel needle-like inclusions reflect a single moving band of light. Cat's eye chrysoberyl forms in the same environments as alexandrite - pegmatites and metamorphic rocks where beryllium and aluminum are both available. The chatoyant 'cat's eye' effect (a single bright band of light moving across the stone) is caused by dense parallel inclusions of fine rutile needles (silk) within the chrysoberyl crystal.

When these needles are densely packed and uniformly oriented, they scatter light perpendicular to their direction, creating a concentrated line of reflected light on the surface of a cabochon-cut stone. The effect is strongest when the stone is cut as a cabochon (domed, not faceted) with the needle inclusions parallel to the base. A well-cut cat's eye shows a sharp, bright line that moves smoothly across the dome as the stone is rotated.

The most prized cat's eye effect is called 'milk and honey' - when a penlight is held to one side, one half of the stone appears milky white while the other shows a deep golden honey color, separated by the sharp eye line.

Cat's eye chrysoberyl is identified by its sharp, well-defined chatoyant band (the 'eye') combined with exceptional hardness (8.5). The eye should be straight, centered, and move smoothly. In fine specimens, the 'milk and honey' effect is diagnostic.

Distinguish from cat's eye quartz (much less sharp eye, lower hardness), cat's eye tourmaline (lower hardness, different colors), and cat's eye apatite (much softer). When gemologists say 'cat's eye' without qualification, they mean chrysoberyl - all other chatoyant stones must be specified (e.g., 'cat's eye quartz').