A gemstone does exactly one thing: it strengthens its planet. That sounds harmless until you ask what the planet is doing in your chart. Strengthening a planet that rules your 6th, 8th or 12th house strengthens obstacles, illness and loss along with everything else.
Weak is not the same as needing a stone
The common advice is to wear a stone for your weakest planet. That is only half a rule. The correct question is whether the weak planet rules something you want strengthened. A weak Jupiter ruling your 5th and 9th is worth supporting. A weak Saturn ruling your 6th and 7th is a different proposition, and the texts advise against it.
Combinations to avoid
- Ruby with Blue Sapphire, Diamond or Hessonite — Sun against Saturn, Venus and Rahu.
- Pearl with Blue Sapphire, Hessonite or Cat's Eye.
- Red Coral with Diamond, Emerald or Blue Sapphire.
- Emerald with Red Coral or Pearl.
- Yellow Sapphire with Diamond, Blue Sapphire or Hessonite.
- Diamond with Ruby, Pearl or Red Coral.
The principle behind the list is planetary enmity. Wearing stones for two planets that are enemies puts the conflict on your own hand and generally produces the symptoms of both being disturbed.
Blue Sapphire deserves its reputation
Neelam is the fastest-acting stone and the riskiest. The tradition is unanimous that it should be trialled — worn against the skin for three days, sometimes stitched into a pillow — before being set and worn permanently. If sleep, health or circumstances deteriorate in those three days, it is removed and not worn again.
Weight, metal, finger and day
A stone must touch the skin to be considered active, which is why settings are open at the back. Weight is prescribed in ratti, the metal is chosen to suit the planet, and the first wearing is timed to the planet's weekday and usually its hora. None of this compensates for choosing the wrong stone in the first place.
Check the house a planet rules before you strengthen it. That single step prevents most of what goes wrong with gemstone advice.