Mineral
Ferroactinolita
Ca₂Fe₅Si₈O₂₂(OH)₂ · Silicato [Inosilicato (Grupo anfíbol)]
Ferro-actinolite, Ca₂Fe²⁺₅Si₈O₂₂(OH)₂, represents the iron-rich end member of the tremolite–actinolite series. It is the ferriferous counterpart of actinolite: the dominance of iron accounts for its higher density and its very dark green, greenish-brown or black tones. It usually occurs as prismatic or acicular crystals, or as fibrous aggregates, with a heavier and darker appearance than common actinolite.
Etymology
From the Greek "aktis/aktinos" ("ray"), referring to its fibrous habit; the prefix "ferro-" refers to its iron-rich composition.