Crystals are the ultimate New Age cliche, though when was the last time your astrologer suggested you wear one? In Jyotish, there is a consistent model of nine precious stones relating to the planets and Nodes, even though the rules for prescribing them vary from astrologer to astrologer. This picture is at least clearer than in the West, where there is not even agreement as to which gems relate to which planet.
This state of affairs was not helped in 1912 by the decision of the American National Retailers Jeweler's Association to declare of a list of 'birth stones', according to month. This purely commercial move exploited the public's fascination with astrology and added mystique, and therefore value, to many common semi-precious stones. Their bogus list was widely adopted, muddying the waters of Western astro-gemology for ever afterwards.
This, like other questions of correspondence such as the chakras for instance, makes the subject very difficult to research. One comes across an intriguing online article where the author lays it all down. A grand theory brings in the Chakras, the Tree of Life, Biorhythms, you name it, and the outer planets, Uranus, Neptune and Pluto are ingeniously thrown in too. You finish the article and look for the provenance of the author's claims, only to find it is entirely their own work, based on a personal whim, or dream-induced revelation in which they have cognized the mysteries of the universe.
Yet even when the recommendation comes on good authority, there are differing attitudes to the therapy. Inflated expectation is the first, with a belief that a costly multi-carat ring set in purest platinum is the key to unlimited wealth and fame and a panacea for all life's ills. Should this scenario not play out, the disillusioned wearer then declares that astrological gemstones are all nonsense.
Medieval and Renaissance astrology had many techniques and practices to remedy planetary influence: crystals, amulets and talismans. By association with overt magic or credulous superstition, these methods were driven underground at around the time as astrology's influence began to decline (c.1700). Today, Western astrology is psychologized to the point where, other other than a few herbalists or those promoting a positive mental attitude, astrologers have few practical techniques.
Jyotish gemstones are only one of a number of Upayes, or remedial measures to propitiate the planets. A jyotishi might recommend a mantra, a Vedic ceremony, or a charitable donation in addition to a precious or semi-precious stone. This gem might be for a planetary period (Dasha/ Antardasha), a benevolent natal planet, or a house in a chart whose affairs need a lift, for example wearing the ninth house ruler's gemstone to promote travel and study.
The Vedic planetary gems are:Sun - RubyMoon - PearlMercury - EmeraldVenus - DiamondMars - CoralJupiter - Yellow SapphireSaturn - Blue SapphireRahu - Hessonite GarnetKetu - Chrysoberyl Cat's Eye.
At the most, there are probably only three gems that any one person can safely wear. Ask an expert: prescription is a delicate art and should be undertaken with great care. It is generally advised to strengthen a benefic planet, rather than attempt to rectify a malefic. You do not wish to boost an already difficult influence. For this reason, blue sapphire and coral are treated with caution, along with the stones for the Nodes. Some ascendants can support a Shani (Saturn) or Mangala (Mars) gemstone, but tread carefully, and if there are any problems or bad feeling, remove it.
Choose the correct finger: Sun, Moon and Mars are ring finger; Jupiter is index finger; Venus, Saturn, Rahu and Ketun are the middle finger; Mercury is the little finger.There is a protocol too for wearing the gem for the first time. Happily, Vedic weekdays agree with the Western model: Sun - Sunday, Moon - Monday, Mars - Tuesday, Mercury - Wednesday, Jupiter - Thursday, Venus - Friday, Saturn - Saturday. Find the planetary hour too, if possible and, aloud, say your name, your ascendant and its Nakshatra, and the purpose you are wearing the gemstone for: "I wish to attract all the blessings of [planet's name] for protection and success".
No one gemstone or japa mala will solve everything, but many people do report subtle effects, both personally and in their practical lives as a result of a carefully chosen crystal. Planetary remedies on the whole exist to ward off tomorrow's problems and to create opportunities today. As Patanjali says in the Yoga Sutras: "Avert the danger that has not yet arisen". Fate is ever-present in astrology, but generally negotiable.