The seven metals of alchemy, gold, silver, mercury (quicksilver), copper, iron, tin and lead, are each paired with one of the seven classical planets, and the same symbol serves for both metal and planet: gold with the Sun, silver with the Moon, mercury with Mercury, copper with Venus, iron with Mars, tin with Jupiter, lead with Saturn. The pairing is ancient and remarkably consistent across the Greek, Arabic and Latin alchemical traditions.
This correspondence is one of the foundations of alchemy and astral magic: a metal shares the nature of its planet, so that working with the metal, or with a talisman made of it, is a way of drawing on the planet's power.