Metal, jin, is one of the five phases of the Wu Xing, and it has no counterpart in the four Greek elements, which is one of the clearest signs that the two systems are independent rather than variants of one idea. Metal is associated with autumn, the west, the colour white, the planet Venus and the qualities of contraction, cutting, refinement and decline, the drawing-in after summer's fullness, the harvest and the paring-away. In the generating cycle metal is produced by earth and gives rise to water (metal was thought to attract or produce dew, or as molten metal flows like water); in the controlling cycle metal is melted by fire and itself cuts wood.
In Chinese medicine metal governs the lungs and large intestine, the emotion of grief, the nose and the skin, and the function of taking in and letting go, breath and elimination. Metal's symbolism is of structure, clarity, righteousness and the incisive, the blade and the boundary, and of the autumnal turn toward stillness, the letting-go that precedes the water phase of winter.
Sources Science and Civilisation in China, Volume 2: History of Scientific ThoughtJoseph Needham with Huangdi Neijing (The Yellow Emperor's Inner Classic)Traditionally attributed to Huangdi; actual authorship unknown