Kelbonite

From Hidden Frontier

Kelbonite is a refractory metal capable of deflecting or interfering with certain types of scans and energy beams, including the transporter. It can be found naturally within caverns and tunnels on many planets.

Ba'ku has mountains that contain kelbonite, which helped prevent the Son'a from removing them from the planet. The atmospheric cooling devices left on the planet by the Breen also contain quantities of kelbonite, a material they are known to use in quantity. (HF 2.06 - "To The Stars")