Stilpnomelane is a common mineral in low-grade metagreywackes and blueschist-facies rocks, as well as in metamorphosed iron formations.  It has high relief and is strongly pleochroic, commonly in shades of yellow to dark brown as seen in images A and B (rotated 90 degrees relative to one another) and D.  The darker regions in D indicate a higher ferric iron content of the stilpnomelane.  It has a micaceous habit and commonly occurs in sheaves or radiating bundles.  Extinction is essentially parallel to {001} cleavage, and a second less well-developed cleavage may occur at right angles to the {001} cleavage.  The interference colours of stilpnomelane range much higher (to fifth or sixth order) than do those of biotite, with which it can be confused.  The interference colours are commonly masked by the strong absorption colours (C).  Features that allow distinction between stilpnomelane and biotite include: a) the {001} cleavage of stilpnomelane is not as well-developed as it is in biotite, b) stilpnomelane can have a second cleavage that is not present in biotite, c) the interference colours of stilpnomelane can be higher than those of biotite and d) the “crinkly” appearance of biotite near extinction is less well-developed in stilpnomelane.  A, B and C are from a stilpnomelane-garnet schist from the Franciscan Formation, California and D is from a retrograded eclogite from Pinchi Lake, B.C.  All fields of view are 5.5 mm across.  A, B and D ppl, C x-nicols.