Rubellite is the red or pinkish-red variety of tourmaline, a crystalline boron silicate mineral.

It exhibits pronounced dichroism, meaning it is characterized by two colors: a primary color and a secondary color. Its color is due to the manganese present in the crystal: a higher manganese content results in a deep red.

Rubellite exhibits birefringence, and lower-quality specimens often have various inclusions visible even to the naked eye. The stone is distinguished by a hardness of approximately 7½ on the Mohs scale, a specific gravity of 3.03–3.25 g/cm³, and a trigonal crystal system.

Excluding the red diamond, ruby, and red spinel, rubellite is one of the most important naturally occurring red gemstones.