Double Refraction Yellow Calcite - IA2Also called Iceland Spar this specific calcite crystal is a birefringent substance. It can split unpolarized light into two different paths, creating a double vision effect on the opposite end of the crystal. Ancient Egyptians used them in the pyramids, Vikings used them in navigation to locate the sun at sea and pilots in World War II used them in the sights of their weaponry. These were acquired in India. The images you see will be the exact