A gemstone is a planetary amplifier — it strengthens whatever planet it represents. That is exactly why the wrong stone is dangerous: amplify a malefic planet in your kundli, and problems multiply. Never wear a gemstone on hearsay.
The correct process: identify your karaka and yogakaraka planets, check their strength and dasha relevance, then choose the stone, weight, metal and finger accordingly — and energise it on the right day with the right mantra. A neelam that transforms one person’s career can wreck another’s health; the kundli decides.
Get your gemstone recommendation only after proper analysis.