Zoisite is a mineral typical of medium grade calc-silicate metamorphic rocks.  It is colourless in thin section and has high positive relief relative to quartz and feldspar.  In image A it stands out relative to enclosing magnesian chlorite and white mica.  It occurs as granular aggregates or in stubby prisms elongate parallel to “b” (A, B) and has a single perfect cleavage on {010}, but this is not obvious in these images.  Maximum interference colour is usually lower first order, and  anomalous blue interference colours (B) are common.  Zoisite is orthorhombic and has extinction parallel to crystal length, unlike the inclined extinction of the monoclinic polymorph clinozoisite. A Mn-bearing variety of zoisite, termed thullite, is pleochroic in shades of pink and yellow (C, D).  A and B are from a glaucophane schist near the Praborna manganese mine, Italian Alps and C and D are from an unknown location.  Fields of view are 2.2 mm across.  A, C ppl, B, D x-nicols.