Chloritoid Occurrence and Composition  Chloritoid is found in low- to meidum-grade metasedimentary rocks. It has general compostion (Fe,Mg,Mn)Al2SiO5(OH)2. It is a layered silicated, similar to chorite and to micas in some ways. Identification  Keys to identifying chloritoid are its relatively high relief, single cleavage, greenish color, and low-order or anomalous interference colors. If visible, an "hourglass" structure, due to zoning, is diagnostic. Important properties  ·Appearance and habit - Chloritoid appears superficually like chlorite but has much greater relief.  ·Color - Choritoid has any of a number of colorations but is typically green and pleochroic. Color zonation, with or without an "hourglass" appearance is common.  ·Interference colors - Maximum colors are first order yellow; somewhat anomalous interference colors are common.  ·Twinning common - Simple or parallel twins are common. Similar minerals  ·Chloritoid has similar color and interference colors as chlorite, but has significantly greater relief.  ·May occasionally be confused with green biotite or stilpnomelane. But both of these have greater birefringence.

Garnet and Chloritoid in a Muscovite Schist from near Poughkeepsie, New York These views shows a blade of choritoid (right center). Note its relatively high relief, cleavage (seen in PP), twinning, and first order interference colors (in XP). Also present are fine-grained muscovite intermixed with some minor graphite, and a large euhedral garnet (isotropic in the XP view). A small flake of biotite is between the garnet and the chloritoid. The fractured garnet contains two flakes of graphite, visible in the PP view. The field of view is 3.5 mm across.