Strange matter

Strange matter was a substance that was the result of or could create spatio-temporal anomalies. (PROSE: Spiral Scratch) Strange matter was related to quarks and was very dense. Small pieces could weigh as much as a planet. Colliding two pieces of strange matter could create a Time Manipulator. (TV: Time and the Rani) An unnamed planet was protected from outsiders by strange matter. (PROSE: Vanishing Point)

Casts could absorb radiation from their vicinity and change it into strange matter, enabling them to exist in two, one or zero dimensions, essentially making them invisible. (PROSE: The Book of the War)

Manipulating strange matter
The Rani attempted to discover the secret of manipulating strange matter on the planet Lakertya through the use of several intelligent beings including the Doctor (who had recently regenerated into his seventh incarnation). The Rani ultimately discovered the key to manipulating strange matter, but was prevented from implementing her ideas by the Doctor's intervention. (TV: Time and the Rani)