pinakiolite
/pɪˈnakɪəlʌɪt/Mineralogy
noun
A mineral that is a borate of manganese and magnesium, Mg2MnO2(BO3), occurring as tabular black crystals of a metallic appearance that belong to the monoclinic system.
Origin
Late 19th century; earliest use found in American Journal of Science. From ancient Greek πινάκιον small tablet (from πινακ-, πίναξ + -ιον, diminutive suffix) + -lite, after German Pinakiolit.