Glaucophane is the blue Na-rich amphibole that is characteristic of the blueschist metamorphic facies.  Views A and B illustrate pleochroism of glaucophane in shades of blue/violet.  The interference colours in C show the maximum of second order blue.  In D the prominent elongated grain (strongly zoned in colour) is cut approximately parallel to the c axis and the small euhedral grain exhibits typical amphibole form perpendicular to the c axis. The dark rims may be enriched in Fe³⁺ and closer to crossite in composition.  A, B, and C are from a garnet-bearing glaucophane schist from Qunicinetto, Italy, and D is from a retrograded eclogite from the Tintina Trench, Yukon Territory, Canada.  All views are 2.2 mm across.