Pendulum - Instrument used for dowsing
People who use a pendulum believe that the answer to every question an individual may ever ask is already in their subconscious mind. They believe that a pendulum can be used to form a link with this information on a very subtle level. The information a pendulum gives us - usually in the form of 'yes' or 'no' answers - through the manner of its rotation, can then help in pursuits such as finding missing objects, locating ley lines (energy lines in the earth), locating weaknesses or strengths within the human aura and helping us to make decisions.
A pendulum should not be used as a crutch to help us decide every which way to go in life. It should be used with the intention to truly help us grow, always seeking answers that can contribute to the greater good.
If you wanted to, you could use a stone attached to a piece of string as a pendulum. The reason there are different styles and shapes is purely for preference. Simply choose the shape and material that appeals to you. For a crystal pendulum you may choose a stone that has qualities that you wish to see appearing more in your life.

Amethyst - Spiritual, calming
The wonderfully coloured amethyst, with its variety of shades of purple reminds us of the spiritual thread that runs through our life and can be used as a tool to aid spiritual awakening and intuition. Amethyst can bring a calming influence and therefore be of great help in times of change. It's excellent to hold or have by you when you're practicing meditation and when placed in a room it can help absorb negativity. Placed under the pillow it may help you sleep better.