Tremolite (Mg/(Mg+Fe) > 0.90) is the Mg-rich end member of this solid solution series, and actinolite (Mg/(Mg+Fe) = 0.90-0.50) refers to compositions intermediate between tremolite and ferroactinolite (Mg/(Mg+Fe) < 0.50).  Tremolite occurs in low to medium grade metamorphosed dolomitic limestones in regional and contact settings.  Actinolite is a low grade mineral, characteristic of greenschist facies metamorphic rocks.  The moderate to high positive relief of these amphiboles is illustrated in images A and C.  In A, longitudinal and basal sections of colourless tremolite blades stand out relative to surrounding talc.  In C pale green slightly pleochroic prismatic actinolite is set in a matrix dominated by low relief colourless plagioclase. The maximum interference colours of second order blue are evident in B and D.  Tremolite and actinolite have inclined extinction.  A and B are from a talc-tremolite schist from Madoc, Ontario and C and D are from a greenschist metabasalt from an uknown location. All fields of view are 2.2 mm.  A and C ppl, B and D x-nicols.