Main members – tremolite (Ca 2 (Mg 5.0-4.5 Fe 0.0-0.5 2 +) Si 8 O 22 (OH) 2), actinolite (Ca 2 (Mg 4.5-2.5 Fe 0.5-2.5 2 +) Si 8 O 22 (OH) 2). Optical characteristics – colourless (tremolite) to green (actinolite), weak pleochroism, prismatic habit, high positive relief, distinct cleavage parallel to c-axis, crossing at 60/120-degree angles in cross sections perpendicular to the c-axis ...