Magnasite-nitron tablets were an item of 23rd century survival gear sometimes found in medical kits. They were small (about 0.5 cm), white, round tablets containing compressed chemicals. Placed on a hard surface and struck with moderate force, they would ignite, burning with a thin flame approximately 25 cm tall. Such a flame was chiefly useful as a light source in darkened areas – it was too small to be an effective heat source. Their small size made them more useful than a portable light in some situations.
In 2267, while fleeing Capellan pursuers on Capella IV, Kirk, Spock, and Leonard McCoy used such a tablet to illuminate their cave refuge, making McCoy's obstetric tasks easier and safer. (TOS: "Friday's Child")