Cat's Eye Moonstone

Cat's eye moonstone is a moonstone—an alkali feldspar, usually orthoclase with adularescence—that has been cut to show chatoyancy, a single bright band of light that glides across the dome like the slit pupil of a cat's eye.

The gem combines two optical effects: the soft, billowy blue-to-white adularescent glow characteristic of moonstone, and the sharp cat's-eye line caused by light reflecting from parallel inclusions or lamellae.

It is always cut as a cabochon to display the effect, and fine stones that show both a clear eye and good adularescence are especially prized.

Moonstone forms as orthoclase and albite feldspar in slowly cooled igneous rocks such as granite and pegmatite, and in some metamorphic rocks. As the feldspar cools, it unmixes into alternating microscopic layers of two feldspar phases (exsolution lamellae).

Light scattering from these layers produces the adularescent sheen, while light reflecting off a set of parallel, needle-like inclusions or aligned lamellae creates the chatoyant band.

Gem moonstone, including cat's eye material, comes mainly from Sri Lanka, India, Myanmar, Madagascar, and Tanzania, where suitable feldspar crystals occur in pegmatites and alluvial gem gravels.

Look for a translucent feldspar cabochon showing a single sharp band of light that moves when the stone is rotated, often with an underlying bluish or white floating glow. Hardness is about 6-6.5 and luster is vitreous to slightly pearly.

The eye in moonstone is typically softer and less crisp than in chrysoberyl cat's eye (cymophane), which is harder (8.5) and more valuable. Quartz cat's eye is also harder (7) and usually lacks adularescence.

To distinguish moonstone, check for its lower hardness, feldspar cleavage, and the characteristic billowy sheen alongside the eye; identical-looking glass imitations lack true chatoyancy and feldspar structure.

Cat's eye moonstone is used exclusively as a gemstone, cut into cabochons for rings, pendants, and earrings. Its value rises with the sharpness of the eye, the strength of the blue adularescence, and the transparency of the body.

Moonstone has long carried metaphysical associations with intuition, emotional balance, new beginnings, and lunar/feminine energy; cat's eye stones are additionally regarded by some as protective. These beliefs are cultural rather than scientific.

It is a popular collector and designer stone, valued for its mysterious, shifting light.