Navaratna: The Nine Planetary Gemstones
Each of the nine classical gemstones: the planet it represents, who traditionally wears it, how it is worn, and the cautions that come first.
Gemstones strengthen, they do not fix
A gemstone amplifies its planet's results in every house that planet rules in your chart, including the difficult ones. That is why classical practice recommends a full chart review before wearing one, and why many astrologers prefer mantra, charity or lighter substitutes when a planet rules a challenging house.