Actinolite-Tremolite Series

Tremolite is defined as having an Mg/(Mg+Fe²⁺) ratio ≥ 0.9; actinolite (retained for petrological reasons) has a ratio of 0.5–0.9 and ferro-actinolite has a ratio of less than 0.5 (Leake et al., 1997; Hawthorne et al., 2012). See also Actinolite-Ferro-actinolite Series. Notes on the formula of the series: The actinolite-tremolite series is defined as a minerals in the calcium amphibole subgroup with ^A(Na+K+2Ca)≤0.5 apfu and ^C(Al+Fe³⁺ +2Ti)≤0.5 apfu. The individual minerals are defined based on the Fe²⁺/Mg ratio in the Z position (= IMA C position) and whether (OH), F or Cl is dominant. In mindat.org we avoid using variables with the same symbol as elements and deviate from the IMA nomenclaure in that we use X rather than B, Z rather than C and (OH,F,Cl,O) rather than W.