Virgo: Lord of 2nd and 9th houses, Venus is auspicious.In the stars of Mercury,Jupiter and Venus it also becomes yogi.Use of diamond is beneficial especially if Venus is in its own sign and running period is of Venus itself. They may use Emerald along with diamond as a life time gem.
Libra: lagnesh Venus with mooltrikona sign in lagna has to be beneficial and hence diamond is suitable. In the stars of Venus and Saturn it is yogi. Venus when located in lagna itself gives malvaya yoga. One may use diamond along with Blue Sapphire.
Scorpio: Enemy of lagnesh and kendra lord Venus becomes malefic. There is no indication of wearing diamond for these natives.
Sagittarius: Lord of 6th and 11th houses again Venus is a malefic. One should not think about diamond unless the running period is Venus’s main and Venus is positioned in its own sign or 10th house (Amala yoga created ) otherwise an inauspicious gem.
(Sun+Venus in 9th is a yoga creating combination.)
Capricorn: 5th and 10th lord of Venus is a yogakaraka and further becomes more benefic if situated in Mercury or Venus’s stars. Placing of Venus is 5th and 10 houses and running Venus’s period is a highly ideal condition of using diamond. It is a strongly recommended gem for this lagana.
Aquarius: Again lord of 4th and 9th Venus is a yogakaraka and also becomes more benefic in the stars of Venus and Mercury. It is a must for them.
Pisces: Lord of 3rd and 8th Venus is an inauspicious planet and they should never use diamond.
More about Diamond
Usually ladies use diamond as part of jewellery without consulting an astrologer. It is a warning to everyone in such cases that the under surface of the diamond should be closed, if they are inclined to use diamond. It is never worn on poornima or prathami of Shukla paksha.
It is worn in gold or platinum ( more preferred). It is highly precious and the weight may range between 10cent to 20cent. Friday is best suited if it falls on Bharini, purvashada and P. phalguni stars. Timing is 10:30 – 12:00 hours and finger is third.
One should never use Ruby, Coral and Pukhraj along with diamond. The pooja should be done with white flowers and mantra “Om darang dareng darong sau shukraya nameh” should be recited ideally 16000 times. Articles to be donated are ghee, silken clothes, rice, etc. to young girls. In my opinion if one cannot afford a diamond or scared of its side effects they may use a big zircon or white sapphire (preferred).
Reference: Gem Therapy in Vedic Astrology: Dr. Neeraji Lalwani