Nystromite was a material that made up onyx-hued crystalline asteroids discovered by the USS Enterprise within the Nystrom Anomaly. A unique property of Nystromite is it's ability to absorb nearly all forms of energy, including graviton's, the emissions from sensors and the majority of stellar emissions, except for light in the visible spectrum. Therefore while invisible to sensors, it was visible to the naked eye.
A piece of Nystromite was brought on board for study, but due to the substance's energy absorbing properties, the Nystromite was unable to be beamed on board with the transporter, or with a tractor beam. Instead a grappler was used to bring the fragment onto the shuttlebay. Further tests revealed, that while the substance was resistant to energy weapons, it was easily shattered with kinetic energy.
Nystromite was also utilized as a weapon by the Taarpi, a rebel organisation within the Goeg Domain. During the Enterprise's investigation of the Anomaly, the ship travelled to the fourth planet in a star system within the Anomaly, having picked up subspace radio transmissions. Whilst in orbit, the ship was attacked by Nystromite asteroids that had fusion rockets mounted on them, turning them into kinetic weapons. The collisions inflicted severe damage to the Enterprise and disabled warp drive. (TOS novel: The Shocks of Adversity)