Nambulite is a lithium bearing manganese silicate mineral with the chemical formula (Li,Na)Mn4Si5O14(OH).

[2] It is named after the mineralogist, Matsuo Nambu (born 1917) of Tohoko University, Japan, who is known for his research in manganese minerals.

[6] The mineral was first discovered in the Funakozawa Mine of northeastern Japan, a metasedimentary manganese ore.[2] Nambulite is formed from the reaction between a hydrothermal solution and rhodonite, and commonly creates veins in the host rock.

The maximum birefringence is .023, the difference between the highest (nc = 1.730) and lowest (na = 1.707) indices of refraction within the mineral.

Relief is a measure of the difference between the index of refraction of the mineral and that of the medium (often Canada balsam or other epoxy with an RI of around 1.53–1.54).