Macdonaldite

Macdonaldite is a rare barium silicate mineral with a chemical formula of BaCa₄Si₁₆O₃₆(OH)₂·10H₂O. Macdonaldite was first described in 1965 and named for Gordon A. MacDonald (1911–1978) an American volcanologist at the University of Hawaii.

Macdonaldite crystallises in the orthorhombic system. Macdonaldite is anisotropic with low relief.