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.

Rose Quartz - Love and calm
Rose quartz is one of the most popular crystals along with amethyst and clear quartz. It has a calming and soothing energy. It promotes self-love and helps overcome feelings of not being 'good' enough, self-criticism and resentment. It reminds us that when you love yourself and are happy in the moment there is no need for haste. Rose quartz embraces the one true currency of life, love.