Ultra clear and gemmy yaogangxian blue fluorite with rainbow twinkles! Perfect for sunny days or a pocket tumble. The Yaogangxian Mine in China is said to be among the most important deposit ever discovered for centuries. Its mine, composed mostly of granite, is a complex structural belt that intruded Paleozoic and Mesozoic sedimentary rocks during the Late Jurassic, forming 157 to 170 million years ago.