Elements

Neither rare nor earths, these 17 elements are nonetheless difficult and unpleasant to mine and refine. Chemically near-identical, these metals have unique magnetic and optical properties, making them essential in modern technology from fibre optics to wind turbines. So should we worry about China's stranglehold over their supply?(Picture: 20 euro note glows under an ultraviolet light; Credit: Frans Dekkers/Thinkstock)