Chimerium is a rare mineral with natural sensor blocking and phaser reflecting properties. Additionally, it is impossible to maintain a transporter lock on chimerium, but it can be transported via a wide-area beaming, if the transport officer is not worried about introducing quantum errors into organic matter caught in the beam.
Chimerium is only found on the Nalori planet Sarindar. The Federation maintains an strict and exclusive contract with the Nalori Republic to export the mineral. The legally controlled material is even more strictly enforced than the purity of latinum, and lives have been lost and taken to maintain the control. (TNG - A Time to... novels: A Time to Kill, A Time to Heal)