Cat's Eye
A stone showing a single bright band of light that moves across it, like a cat's pupil. The stone of Ketu.
The effect is called chatoyancy, and it comes from parallel needle-like inclusions reflecting light in one line.
It only shows properly in a cabochon, because a domed top gathers the band. Faceting destroys the effect.
Cat's eye chrysoberyl is the true gem. Quartz and other stones also show the effect and must be named accordingly.
When you are buying
The band should be sharp, centred and cross the dome cleanly when you rock the stone. A vague or off-centre eye is worth far less.
Cabochon
A smooth domed top with a flat base, no facets. The only way to show a cat's eye, star or opal fire.
Navratna
A setting of nine gemstones, one for each of the nine planets in Vedic astrology, arranged in a fixed order.
Gemstone
Any mineral or organic material cut for jewellery. Traditionally split into precious (diamond, ruby, sapphire, emerald) and semi-precious.
Moon Dasha
The planetary period ruled by the Moon in Vedic astrology, during which a pearl is most commonly prescribed.