Branzine

Branzine was a mineral used as a power source. For this reason it entailed a high value, with large quantities costing trillions. The Second Doctor considered it an old fashioned and dirty power source.

Jack bought six planets and mined them of their branzine. He imported Halflings to work the mines and rocket ships to transport the mineral to his buyers.

One such planter was Juno 10. The Second Doctor took Jamie McCrimmon and Zoe Heriot and they persuaded Jack to allow them near the large hole on the surface, unaware it was in fact a mine shaft. A second hole opened and they fell in to the shaft.

Worried for his branzine cargo, Jack launched his rocket despite it only being 86.9% full. To his astonishment, it exploded in mid-flight, because of the Doctor's intervention, losing Jack his cargo. (ST: Penny Wise, Pound Foolish)