Sun : Ruby is recommended. Pinkish ruby for women and dark ruby for men.
Moon : Pearls are best for women. Crystals are good for men. However in men , if moon is very strong by being exalted , or is in lagna or is otherwise strong then pearl should be recommended in place of crystals.gem
Mercury : Emerald. Dark green emerald for gemeni and light green for virgo.
Jupiter : Yellow sapphire or Yellow topaz depending upon the temperature balance.Yellow sapphire has very cooling effect. Yellow topaz has heating effect.  The temperature balance should be taken into account before suggesting the gemstone. If temperature goes down then native can fall sick , can acquire cold and fever. In such cases native should be advised to wear gemstones for shorter durations and a permanent gemstone of Jupiter can not be recommended. This temperature balance should be taken into consideration only while recommending gemstones for Jupiter. Other planets do not have any such issues.
Venus : Diamond, the king of gemstones. White coral etc . Venus is always heated up and requires a gemstone that can hold the heat and return it as and when required. White coral is good when the body is having fluid balance problems. Wearing white coral can be recommended when the skin is getting dry and becoming lustreless , fluid imbalance , sleeplessness etc.

Saturn : Blue sapphire, the most dangerous gemstone. It is generally used by royal kings to control servants and demolish the enemies. This gemstone suits very few people as this gemstone automatically calls Saturn. So instead of using this gemstone mantras are recommended.
Rahu : Hessonite or Garnet , also known as Gomed. Rahu will runaway by looking at Gomutra gomed. This is yellow in colour and rahu is very scared of this gemstone. Red or black gomed will invite rahu but they are not good. Gomutra gomed is very good. Garnet is the substitute for Hessonite. Mostly cultured and diplomatic people wear garnets.
Ketu : Cat’s eye or tiger’s eye.Tiger’s eye is for material benefits while cats eye is for spiritual upliftment. This gemstone give ultimate protection from ghost attack. Yellow cats eye is the best.