Mundic, or Marcasite, a species of copper-pyrites found in the tin-mines of Cornwall, and in other parts of the world. It is of various colours, being sometimes yellow, green, or white; but is easily distinguished by its glittering, and frequently contains a considerable portion of copper.

The steams of this mineral are very offensive to the miners ; they are however, reputed to be a good vulnerary, and are the only Temedy employed by the labourers in tin-mines, who wash their wounds in the water which runs from the mundic-ore.