noun.
A mineral with monoclinic crystals of the chemical formula Ca2(Mg,Fe)5Si8O22(OH)2, belonging to the amphibole group.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
a green mineral of the amphibole group; calcium magnesium iron silicate
Word Usage
"In accompanying notes, a geologist identified as W.J. Hunter boasted of a rock formation from the Miocene Epoch that gleamed with boulders of "tourmaline-actinolite-quartz plutonites.""