Gentle cleaning: Start by gently cleaning the tourmaline with mild soap and warm water. Use a soft toothbrush or a soft cloth to remove any dirt or debris that may be contributing to the white coating. Be careful not to scrub too vigorously, as tourmaline can be sensitive to abrasion.

Diluted vinegar solution: If the white coating is caused by mineral deposits or hard water stains, you can try using a diluted vinegar solution. Mix equal parts of water and white vinegar, and soak the tourmaline in the solution for a few minutes. Gently scrub the stone with a soft toothbrush, then rinse it thoroughly with clean water.

Professional cleaning: If the white coating persists or if you are unsure about the cause, it is recommended to consult with a professional jeweler or gemologist who specializes in gemstone cleaning. They will have the expertise and appropriate tools to handle the cleaning process safely and effectively.

Avoid harsh chemicals: It's important to avoid using harsh chemicals, strong acids, or abrasive cleaners on tourmaline, as they can damage the stone's surface or alter its color.