Parrinium was a rare element found in large quantities on the planet Exxilon. Only traces existed on Earth which made it very rare and priceless. After a space plague swept the outer colonies of the Galaxy, it was proven that parrinium was the cure for it. Parrinium not only cured the plague, but it gave immunity and they needed it in quantity.
A human taskforce was sent to Exxilon to mine parrinium and bring it back to cure the millions of sufferers. A Dalek taskforce also went to Exxilon to obtain the ore, but only so that they could blackmail the galaxy into submission. The Daleks enslaved the native Exxilons and forced them to mine the parrinium for them. The Third Doctor, Sarah Jane Smith, and the human expedition tricked the Daleks by loading their ship with sand instead of parrinium. The Exxilons used parrinium as a condiment. (TV: Death to the Daleks)