These orthorhombic amphiboles are miscible at high temperatures and have similar optical characteristics that make it difficult to distinguish between them.  Members of this series have medium to high positive relief relative to quartz, for example, and in A stand out relative to coexisting cordierite.  They commonly form colourless euhedral to subhedral bladed crystals.  Traces of the {110} prismatic cleavage are visible in most grains in A and B, in which the c axes are horizontal), and one grain in the upper right of A exhibits typical amphibole form in basal section.  Interference colours are a maximum of second order blue (B) and extinction is parallel to the trace of {110} cleavage in elongate grains.  Sample from an “anthophyllite”-cordierite rock from the Betty Mine, Guffey, Colorado.  Field of view is 5.5 mm in both images.  A ppl, B x-nicols.