Emerald is useful during transitional times in your life. It assists understanding changes and new directions taken. It can also be used as a cleanser to rid yourself of any lingering negative energies. The planet Mercury is regarded as the prince among the assembly of nine planets. Mercury is the son of the moon by his wife Rohini. In human body Mercury represents wisdom and voice. Mercury is the ruler of two signs of the Zodiac - The Gemini and The Virgo.