Wiktionary
grunerite
n. (context mineral English) An iron-rich amphibole related to cummingtonite.
Wikipedia
Grunerite
Grunerite is a mineral of the amphibole group of minerals with formula Fe Si O( OH). It is the iron endmember of the grunerite- cummingtonite series. It forms as fibrous, columnar or massive aggregates of crystals. The crystals are monoclinic prismatic. The luster is glassy to pearly with colors ranging from green, brown to dark grey. The Mohs hardness is 5 to 6 and the specific gravity is 3.4 to 3.5.
It was discovered in 1853 and named after Emmanuel-Louis Gruner (1809–1883), a Swiss-French chemist who first analysed it.