Gemstones are minerals in crystal form which can influence the environment with their electromagnetic field and have energising properties. They have been prescribed for healing and energising the human body from ancient times in all cultures. Specific mention of the use of gemstones have been mentioned in the Rig Veda and many Puranas (historical texts) such as Gaurda, Agni and Kurma Purana. The use of gemstones is called Tantra as it involves the physical and mental plane of body. Each prescribed gemstone represents the energy of the planet and harnesses that energy to bring about needed balances and changes. The overlord of all Gemstones is the planet Moon.
Here is the verse from Jataka Parijata an astrological text that specifically associates the gemstones with the planets.
माणिक्यं दिननायकस्य विमलं मुक्ताफलं शीतगतोः
माहेयस्य च विद्रुमं मरकतं सौम्यस्य गारुत्मतम्।
देवेज्ययस्य च प पुष्परागं असुराचार्यस्य वज्रं शनेः
नीलं निर्मलनन्ययोश्च गदिते गोमेद् वैदुर्यकेः॥
māṇikyaṁ dinanāyakasya vimalaṁ muktāphalaṁ śītagatoḥ
māheyasya ca vidrumaṁ marakataṁ saumyasya gārutmatam |
devejyayasya ca puṣparāgaṁ asurācāryasya vajraṁ śaneḥ
nīlaṁ nirmalananyayośca gadite gomed vaiduryakeḥ ||
Ruby is the gem of the Lord of the day, Sun
Spotless pearl is the gemstone of the Cool Moon
Red Coral is the gem of Mars (made of earth)
Emerald is the gemstone of Mercury like the bird Garuda
Yellow Sapphire is the gem of Jupiter, the preceptor of the divine
Diamond is the gem of Venus, the teachers to the demons
Blue Sapphire is the gem of Saturn
Hessonite and Cats eye are the gemstones of the remaining planets Rahu and Ketu
|Planet||Primary||Substitute||Min Size (carats)||Metal||Finger||Day|
|Sun||Ruby||Red spinet, red tourmaline||2.5||Gold||Ring||Sunday|
|Moon||Pearl||Moonstone, Quartz||1.77||Silver or White Gold||Little||Monday|
|Mars||Coral||Carnelian, Red Jasper||6||Gold||Ring||Tuesday|
|Mercury||Emerald||Peridot, green agate, jade green tourmaline||3||Gold, Silver or White Gold, platinum||Little||Wednesday|
|Jupiter||Yellow Sapphire||Yellow topaz, citrine||3||Gold||Ring||Thursday|
|Venus||Diamond||White sapphire, white tourmaline||1.5||White Gold or Platinum||Ring||Friday|
|Saturn||Blue Sapphire||Amethyst, lapis lazuli, Blue spinel||5||White Gold or Silver||Middle||Saturday|
|Rahu||Hessonite||Garnet||5||Mix of Metals, Gold or Silver||Middle||Saturday|
|Ketu||Cats eye||Opal||5||Mix of Metals, Gold or Silver||Middle||Tuesday|
Gemstones can be used to strengthen the properties of weaker planets, however care must be taken to ensure that it is suitable to the overall horoscope. If the planet for which the gemstone is worn is placed badly or has ill aspects it will only bring more troubles. Gems worn for benefic planets enhance auspicious qualities when placed in the right houses whereas malefic planets enhance more masculine attributes. The Gemstone of the lord of the ascendant sign is considered lucky, however we should study its house placement to see the effect it will generate. The gemstone of the lord of the sign in which the Moon is placed is also considered fortunate, again care should be taken to see whether this lord is not ill placed. Different gemstones can be chosen to for different planetary periods.
A gemstone can be only effective if it is natural and not heat-treated or chemically treated. It has to be of the right lustre, flawless as possible and of the appropriate size to make a difference. It has to be also set with the appropriate metal. The gemstone has to worn on an auspicious day appropriate for the gemstone and deity of the gem needs to be worshipped before wearing it for good results.