Talc Occurrence and Compostion  Talc is found in some marbles and as an alteration product in mafic and ultramafic rocks. In marbles it is often associated with tremolite. In mafic/ultramafic rocks it may be found with other Mg-silicates (e.g., olivine) or hydroxides (e.g., brucite). Identification  Talc is similar to muscovite. It is clear and has high birefringence, Distinguishing talc from muscovite or other white micas may be difficult. It is often identified by association with other minerals present in a sample. Important properties  ·Appearance and habit - Talc appears similar to many other white micas. It may form flakes or aggregates and often displays a single cleavage.  ·Color - clear  ·Interference colors - Third order colors are typical. Similar minerals  ·Can be easily confused with muscovite or other white micas. Sometimes it may appear to have greater birefringence than typical muscovite. It may also have a more patchy or zoned appearance than other white micas when viewed in XP.

Talc in a Serpentenite (Verde Antique) This photomicrograph, about 2 mm across, is of a serpentenite from Windsor County, Vermont. Most of the photo shows antigorite (serpentine; clear to light green PP, 1st order interference colors XP). The material forming a sickle-shaped patch near the center, showing higher relief and very high order interference colors, is talc. Some patchy magnetite (opaque) can be seen near the right edge.

Talc with Minor Tremolite in a Schist This is a talc-tremolite schist from the Adirondack Mountains, New York. Most of this view is talc; only minor tremolite is present in the lower right of the photo (showing 2nd order yellow interference colors in XP). The tremolite, difficult to see in the PP view, stands out in the XP view because the interference colors are significantly lower order than talc's. The field of view of these photos is about 2.5 mm.

Talc with Tremolite in a Schist This is a talc-tremolite schist from the same location as the previous photos. The tremolite is clear in PP light and has 2nd order interference colors in the PP view. The talc, which has a dingy green color in the PP view shows extremely high order interference colors -- almost "pearl white" in the XP view. The field of view of these photos is about 2.5 mm. This thin section was poorly made. Many small bubbles were trapped in the epoxy when it was prepared. They appear as small round circles in these pictures.