The Collaborative International Dictionary of English v.0.48:

Actinolite \Ac*tin"o*lite\, n. [Gr. ?, ?, ray + -lite.] (Min.)
   A bright green variety of amphibole occurring usually in
   fibrous or columnar masses.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Amphibole \Am"phi*bole\ ([a^]m"f[i^]*b[=o]l), n. [Gr.
   'amfi`bolos doubtful, equivocal, fr. 'amfiba`llein to throw
   round, to doubt: cf. F. amphibole. Ha["u]y so named the genus
   from the great variety of color and composition assumed by
   the mineral.] (Min.)
   A common mineral embracing many varieties varying in color
   and in composition. It occurs in monoclinic crystals; also
   massive, generally with fibrous or columnar structure. The
   color varies from white to gray, green, brown, and black. It
   is a silicate of magnesium and calcium, with usually
   aluminium and iron. Some common varieties are tremolite,
   actinolite, asbestus, edenite, hornblende (the last
   name being also used as a general term for the whole
   species). Amphibole is a constituent of many crystalline
   rocks, as syenite, diorite, most varieties of trachyte, etc.
   See Hornblende.
   [1913 Webster]

WordNet (r) 3.0 (2006):

actinolite
    n 1: a green mineral of the amphibole group; calcium magnesium
         iron silicate