The main purpose of wearing a gemstone, especially in India, is to get astrological benefits out of it. When we say astrological gemstones, we are referring to the gemstones or ratnas mentioned in the holy texts. According to the Indian Vedic Astrology, there are 7 main planets and 2 intersection points which gives a sum of total 9 astrological bodies called Nava-Grahas.
Sun, Moon, Mars, Mercury, Jupiter, Venus & Saturn are those 7 planets and the two intersection points are called Rahu & Ketu.
It is believed that these Nava-Grahas have substantial significance in a human life. As we all know, the water tides in oceans are controlled by the gravitational force of moon, since 70% of a human body is believed to be made up of water content, it may be logical to believe that Moon has its own effect over the human body as well. Just like the moon, every other planet has its own gravitational force which directly or indirectly affects the human body and life.
Astrologers analyze the birth charts of individuals and recommend certains planetary positions as weak or strong and as a remedy to give strength to those weaker planets in a horoscope, they suggest few gemstones. According to Vedic astrology, the gemstones associated with these Nava-Grahas are called Nava-Ratnas. They are Ruby for Sun, Pearl for Moon, Corals for Mars, Emerald for Mercury, Yellow Sapphire for Jupiter, Diamond for Venus, Blue Sapphire for Saturn, Hessonite for Rahu and Cats Eye for Ketu.
One must definitely get her/his horoscope checked thoroughly by a professional and qualified Vedic astrologer before wearing a gemstone because every gemstone has a positive as well as a negative energy which can benefit as well as harm a human life.