In the Vedic astrological system known as Navaratna — the nine-gem configuration believed to represent the celestial bodies of Jyotish cosmology — chrysoberyl cat's-eye is the stone assigned to Ketu, the descending lunar node. Ketu is classified as a chhaya graha, or shadow planet, representing the point at which the Moon's orbit crosses the ecliptic in a southward direction. Unlike the seven visible planets of the Navaratna, Ketu has no physical body; it is a mathematical point, and its associated gemstone reflects this liminal, otherworldly character. The chrysoberyl cat's-eye — known in Sanskrit as vaidurya and in Hindi as lehsunia — is among the most optically dramatic of all gemstones, and its association with a node rather than a planet gives it a distinctly esoteric standing within the tradition.

Ketu in Vedic Astrology

Ketu and its counterpart Rahu (the ascending node, associated with hessonite garnet) are treated in Jyotish as full planetary influences despite their astronomical nature as orbital intersection points. Ketu is associated with spiritual liberation (moksha), past-life karma, renunciation, and sudden or unexpected events. In a natal chart, a well-placed Ketu is said to confer intuition, detachment, and occult insight; an afflicted Ketu is linked to confusion, loss, and psychosomatic illness. The prescription of a gemstone is intended to strengthen or stabilise Ketu's influence, and is traditionally made only after careful horoscopic analysis by a qualified Jyotishi.

The Gemstone: Chrysoberyl Cat's-Eye

The stone prescribed by classical texts is unambiguously natural chrysoberyl cat's-eye — Chrysoberyl (BeAl₂O₄) exhibiting the optical phenomenon known as chatoyancy. This effect arises from dense, parallel inclusions of fine rutile or hollow growth tubes oriented along the crystal's length; when cut as a cabochon, these inclusions reflect incident light as a single luminous band that moves across the dome as the stone is rotated, resembling the slit pupil of a cat's eye. Chrysoberyl is one of the hardest gemstone minerals (Mohs 8.5), and its chatoyancy is among the sharpest and most mobile of any gem species, which is why it has historically commanded the designation "cat's eye" without qualification in the trade — other chatoyant stones require a species prefix (tourmaline cat's-eye, quartz cat's-eye, and so on).

Traditional Vedic texts specify several qualitative criteria for a suitable lehsunia:

• A sharp, well-centred, and mobile eye that divides the stone cleanly into two equal halves
• A body colour ranging from honey-yellow to greenish-grey or milk-and-honey — the finest stones display the so-called "milk and honey" effect, in which one half of the stone appears milky white and the other golden when a single light source is directed at the gem
• High transparency in the body, free of cracks, cloudiness, or distracting secondary inclusions
• Natural, untreated origin — heat treatment or fracture filling is considered to negate the stone's astrological efficacy

Principal Sources

The most historically significant source of fine chrysoberyl cat's-eye is Sri Lanka (Ceylon), which has supplied the gem trade for centuries and continues to produce stones of exceptional quality, particularly from the gem gravels of Ratnapura and Elahera. Brazil (notably Minas Gerais) is a major modern source. India's own deposits, primarily in Orissa and Andhra Pradesh, have produced material of variable quality. Smaller quantities have been recorded from Zimbabwe, Tanzania, and Madagascar.

Setting and Wearing Traditions

Classical prescriptions advise setting the cat's-eye in silver or gold — authorities differ on which metal is preferable for Ketu — and wearing it on the middle finger of the right hand. The stone is traditionally activated through a consecration ritual (prana pratishtha) performed on an auspicious day, often a Tuesday or Saturday associated with Ketu's influence. Weight recommendations vary by practitioner but commonly fall in the range of three to five carats minimum, with larger stones considered more potent.

Gemmological Identification and Simulants

Because chrysoberyl cat's-eye commands significant premiums — particularly for fine Sri Lankan material with a sharp eye — the market contains numerous simulants. Quartz cat's-eye (fibrous quartz or "tiger's-eye" cut as a cabochon) is the most common substitute and is far less valuable; it can be distinguished by its lower refractive index (approximately 1.54–1.55 versus chrysoberyl's 1.74–1.75) and its softer, less crisp chatoyant band. Glass fibres and synthetic chrysoberyl have also appeared. Laboratory identification by a recognised gemmological laboratory is strongly advisable before any stone is purchased for astrological use, as the tradition holds that only a natural, genuine chrysoberyl produces the intended planetary effect.