Silver and the Moon
Silver exists in its pure form within the earths crust, meaning that people have been aware of it for thousands of years. Over this time, the metal has accumulated meanings and uses, both symbolic and practical, of many kinds.
One well known pairing of silver is with the moon. The chemical symbol of silver, Ag, comes from the Latin argentum, which means off-white. It is this colour which is thought to be the main reason the metal has its association with the moon and its ghostly light. The goddess Artemis, tasked with bringing the moon each night, uses a silver bow in her role as Goddess of the Chase and wears a crescent moon head piece.
The ancient Egyptians considered silver to be a 'near perfect metal', and venerated it as such. They gave gold the symbol of a circle (as the most perfect metal), and silver the symbol of a semi-circle, again tying silver to the image of a crescent moon. The skin of ancient Egyptian Gods was said to be gold, while their bones were made from silver.
Another strong connector is alchemy. In the 1600s, Alchemists connected the seven base metals to the seven planets, and also to parts of the body. Silver is associated to the Moon, and to the brain. This connection is probably what spurred terms such as 'lunacy', which originally referred to changes in behaviour that were thought to be in reaction to the changes in the moon during the month.
In 1614, Angelo Sala gave silver nitrate internally as a counterirritant, a purgative, and for the treatment of brain infections. Later, it was used as a treatment for epilepsy after one patient stopped having seizures after swallowing a silver coin that had been used to try to prevent the patient biting his tongue during a seizure.
Interestingly, while silver was used to treat seizures and brain infections, by the 1900s it was found that high doses of silver could actually cause convulsions and even death, which probably only further enforced the idea that silver, the brain, and the moon have a powerful connection.
Because of their close connection, the moon and silver share lots of symbolic meanings, such as purity and innocence, or a connection to femininity, fertility and protection.