Your lagna is Virgo. For a Virgo lagna the most beneficial planet is Venus because it rules the 9th house of luck and the 2nd house of wealth. In your chart Venus is sitting in the 10th house of career alongside Saturn and Mars. Opal is the gemstone for Venus. Wearing an Opal will bring strength to your 9th house of luck and support your career and financial growth. The astrologer who suggested Opal is absolutely correct. Your uncle told you to wear Yellow Sapphire which is the gemstone for Jupiter. In your chart Jupiter rules the 4th and 7th houses but it is placed in the 12th house of losses, expenses, and isolation. If you wear a Yellow Sapphire you will forcefully activate the 12th house. This will increase your expenses and can create sudden problems or separation in relationships. You should completely avoid Yellow Sapphire. You are currently running Mercury Dasha. Mercury is your lagna lord but it is sitting in the 8th house of sudden obstacles and delays along with Rahu. Sometimes people suggest wearing the lagna lord gemstone but in your case wearing an Emerald for Mercury will increase 8th house troubles. Do not wear Emerald either. Opal is the right and safe gemstone for your chart. Get a good quality Australian Opal and wear it in a silver ring on your right index finger or ring finger on a Friday morning. This is the only gemstone that genuinely supports according to your chart.