A monoclinic mineral, 2(Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂) in the hornblende series Mg/(Mg+Fe₂₊) = 0.5 to 0.89 of the amphibole group; forms a series with tremolite; 42 green, bladed, acicular, fibrous (byssolite asbestos), or massive (nephrite jade); prismatic cleavage; in low-grade metamorphic rocks.