Approximately 1.9 inches.
Fluorite is often referred to as "Genius Stone" due to its ability to help people achieve their goals, acquire new knowledge, and activate both brain hemispheres simultaneously. It is believed that wearing Fluorite may help you achieve perfection through knowledge, help you balance memory, and achieve harmony. 
Fluorite provides emotional balance and stability. Wearing Fluorite will help you handle hard emotional situations. It will clear your mind and help you handling those situations without being overwhelmed. It will also boost your confidence and help you confront and talk to other people in a gentle way.