In the astrology, Gem are consider a big remedial tool, to enhance the power of planets. So all the Astrology system i.e., Indian, Vedic, Chinese, Western or any other Astrology system recommend GEM to enhance power of planets. They are big gift to us by Mother Earth and considered since thousand year . They also play a big role in medical science, in Ayurveda or Unani. Gems are prescribed according to planets in any one's horoscope.
Indian astrology consider Lagna (Ascendant), 5th and 9th house as most auspicious or benefic houses. Lord of these houses are most benefic planets. Indian astrology suggest to wear a Gems , according to planets, who are lords of these houses. Ascendant (Lagna) Lord planet's Gem consider as LIFE STONE or Gem, because this house is significator of our body, health, age, name, fame, status etc. Gem of 9th house lord planet consider as LUCKY GEM, because 9th house is for Luck, fate. Gem of 5th house is also for Luck, as this house called 'Mini Luck house'.
5th house is also signify speculation, art, talent and Health recovery. If we see in degrees, 1st (Ascendant), 5th and 9th house make a triangle in Zodiac, They divide Zodiac in 3 parts, 120 degree each. A triangle have a very important role in all ancient science, Yantra and Pyramid science based on triangle.