White, chalcophile metallic element, with an atomic weight of 107.87 and a specific gravity of 10.7. It is one of the ‘noble’ metal group and is usually found in ores combined with gold and/or copper, as well as with lead and zinc sulphides. In earliest times it was scarcer than gold and was used sparingly for jewellery and smaller objects, often of a mystical nature. Hence it was likened to the moon, given the name Luna by alchemists, and became the symbol of the goddess Diana. As ‘a Mineral of that excellent Nature’ (William Badcock: A New Touchstone for Gold and Silver Wares, 1679), silver has been most valued for its lustre and non-reactivity. It is traditionally valued at approximately 6.6% of the equivalent weight of gold. Silver used to be in heavy demand for most of the world’s coinage and particularly for the photographic industry, while the space industry is still reliant on it.