The effects gems will have depends on the nature of their Planet lord’s attitude or placement in each individual horoscope.  There are two types of planets in every horoscope, viz., ANUKUL-GRAHA or favorable planets, and PRATIKUL-GRAHA or unfavorable planets. Gems will act accordingly. If (for example) Surya (Sun) is well-placed in your horoscope then Sun's gem, ruby, will also act well; but if Sun is ill-placed in your chart then the Sun's gem will also be unfavorable.

Below are simple basic guidelines on how fine quality jyotish gems might influence us.

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1. Influence of Ruby / red spinel ---If Sun is well placed in your horoscope the influence will be toward:  Nobility, dignity, power, leadership, confidence, one will be well-read, pious, strong, compassionate and untroubled. ---If Sun is ill placed in your horoscope the influence will be toward: No self esteem, no energy, no confidence, bucking authority, contrary results may be expected.

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2. Influence of (natural) Pearl / moonstone ---If Moon is well placed in your horoscope the influence will be toward: Good sensitivity, good habits, stability, health, one will be wealthy, industrious and respected. ---If Moon is ill placed in your horoscope the influence will be toward: Over reacting, depressed, overly sensitive, stressed, contrary results may be expected.

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3. Influence of Yellow Sapphire / yellow topaz ---If Jupiter is well placed in your horoscope the influence will be toward:: Humanitarian, caring, spiritual, optimism, faith, good judgment, one will be a leader of men, powerful, respected, although susceptible to anger.  ---If Jupiter is ill-placed in your horoscope the influence will be toward: Greedy, uncaring, selfishness, too pragmatic, negative outlook,  personal unhappiness, egotism, sloth, and legal problems.

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4. Influence of Hessonite / orange zircon ---If Rahu is well placed in your horoscope the influence will be toward: Originality, inspiration, insight, uniqueness, exotic, wealthy and fortunate.  ---If Rahu is ill placed in your horoscope the influence will be toward: Mental disease, addiction, illusion, volatile-nature, trouble, a tendency to suffer from fear of supernatural phenomena and suicidal impulses.

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5. Influence of Emerald / tsavorite ---If Mercury is well placed in your horoscope the influence will be toward: Rational, witty, skill, dexterity, worldly-brains, one will be educated, happy, fortunate and highly respected.  ---If Mercury is ill placed in your horoscope the influence will be toward: Aloof, lack of concentration, difficulty with communications, slow, one becomes prone to speech and hearing impediments, deceptive behavior, and lack of vitality.

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6. Influence of Diamond / colorless quartz ---If Venus is well placed in your horoscope the influence will be toward: Attractiveness, refinement, grace, elegance, smooth, one will be humanitarian, long-lived and possess many good qualities.  ---If Venus is ill placed in your horoscope the influence will be toward: Vanity, lewdness, sensual corruption, lack of taste and refinement, one becomes vulnerable to loss of libido, impotence and sterility, venereal (lit. of Venus) complaints, and rapid aging.

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7. Influence of Chrysoberyl Cat's Eye / fibrolite cat’s eye ---If Ketu is well placed in your horoscope the influence will be toward: Spiritualism, intuition, universality, subtleness, sensitivity, one will be  wealthy and protected from evil.  ---If Ketu is ill placed in your horoscope the influence will be toward: Eccentricity, explosiveness, fanaticism, emotional problems,  one becomes prone to fatal diseases of a mysterious nature as well as  compulsive gambling.

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8. Influence of Blue Sapphire / indicolite (sapphire-blue tourmaline) ---If Saturn is well placed in your horoscope the influence will be toward: Discipline, responsibility, realism, durability, humility, one will be long-lived, charitable, lavish, proficient and an affectionate mate.  ---If Saturn is ill placed in your horoscope the influence will be toward: Depression, anxiety, fear, loneliness, disappointment, one becomes vulnerable to headaches, neuralgia, and other disorders of the nervous system, as well as epilepsy, stupidity, and fainting.

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9. Influence of Red Coral / red carnelian

---If Mars is well placed in your horoscope the influence will be toward: Positive energy, strength, courage, passion, active, one has great energy, is learned, well-known and regal. 

---If Mars is ill placed in your horoscope the influence will be toward: Anger, irritable, over reactive, impatience, aggression, one becomes prone to boils (due to impure blood), unstable blood pressure, anemia, and violence.