Planets and gems - their effect on the humans.

"Planets being visible manifestations of God, the   worship we  offer  them ultimately reaches God" 

                                                                                                                    .......   Jyotisharnava

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Ever since the dawn of civilization, man's inquiry in to the future had begun to shape. Along with the progressive development of sciences - Astronomy, Physics, Chemistry, maths, etc also grew his anxiety about his personal future - his fortunes, misfortunes, etc., over which one one can predict 100 percent. From the additional  study of Planetary  physics, Astronomy, etc  man found out that the there was some kind of relationship between humans and the positions of planets at the time of their birth. This led to the development of Astrology - science of prediction based on the positions of planets  at one's birth. The  discovery of Mineralogy - study of minerals, metals and gems (a part of Geological sciences) went one step ahead and came up with the postulation that, wearing  some gemstones  or the others  very close to the body in propitiation  of some planet or other  with reference to  a particular horoscope is good for the well being of that person. If gems are set in jewelery, they should be set in such a way the Sun's ray should pass through it. Positively it'll have curative effect on the body. Numerous people besides Indians in SE Asia wear Navagraha gems, regardless of religious and cultural significance.

In ancient Hindu text ''Shukraneeti,''an authoritative work deals with details of planetary gems to be worn in conjunction with one's horoscope.

The following are the "Maha-ratnas":

Vajra (diamond), Mukta (pearl), Praval (Coral), Gomeda, Indraneela (Sapphire), Vaidurya (Lapiz Lazuli), Pushparaga (Topaz), Pachi (Emerald) and Manikka (Ruby).

,
The Sun has great affinity for red : RUBY
The Moon has great affinity for colors like red, yellow, white and dark: PEARL

Mars or Mangal loves orange: CORAL

Mercury or Budh loves leafy green: EMERALD

Jupiter or Guru favors yellow or golden: POKRAG, YELLOw SAPPHIRE.

Venus or Sukra- his favorite color is resplendent, star like brilliance: DIAMOND.

Shani or Saturn is is fond of dark color - that of a cloudy dark;SAPPHIRE

Rahu favors light or gentle yellow and red: GOMAED,HESSONITE

Ketu - color of the cat's eye: LAPIZ LAZULI

The above text further elucidates the following:
 
Navaratna is a Sanskrit  word meaning "nine gems". Jewelry made using planetary gemstones  in a particular fashion has important cultural significance in Hinduism, Jainism, Buddhism, and Sikhism, among other religions. The Navagragha rings should be worn with proper care and the gems are set in as per one's horoscope.
 
It is essential to choose flawless gems, gems without microscopic cleavages. Though it is difficult, flaws should be minimum.

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Wearing  flawless gems will bestow good health, fame, confidence, prowess - both mental and physical and above all longevity.

"Pure, flawless gems have auspicious powers which can protect one from demons, snakes, poisons, diseases, sinful reactions, and other dangers, while flawed stones have the opposite effect."
         Garuda Puranam (Chapter 68, verse 17)

Gem stones can be set in a chain or ring  and body contact is essential for necessary effect. if you are a regular oil bath taker, care should be taken to remove the ring or chain before bathing.

If all gems have to be worn on a ring or some pendant, a particular or accredited pattern or arrangement should be followed:

At the center        .......       Sun
At the east           .......       Mars
At the west          .......       Jupiter
At the north-west .......       Mercury
At the north         .......       Venus
At the noth east   .......       Moon
At the south         .......       Saturn
At the south-east  ......       Rahu
At the south-west    :         Ketu        

Our ancient Rishis or learned saint are of the view wearing planetary gems is a way of not only assuaging ailments but also improving our prospect of success in life. After all belief and trust are the deriving forces.

Ref: 
https://en.wikipedia.org/wiki/Navaratna