Amethyst

The gem amethyst, which is often used in jewelry, particularly in India, is actually just a purple-colored quartz. When the quartz is exposed to iron and aluminum it becomes purple.

Historically, people believed the stone protected them from feeling "extreme passion" or emotions. The Egyptians believed it warded off fear, however, it's also known as the "Bishop's Stone" in the Catholic church, representing piety and wisdom.