kentrolite

from The Century Dictionary.

• noun A rare silicate of lead and manganese occurring in southern Chili in acutely terminated crystals, also in sheaf-like aggregates of a reddish-brown color.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy An orthorhombic-dipyramidal mineral containing aluminum, iron, lead, magnesium, manganese, oxygen, silicon, and titanium.