Staurolite Occurrence and Compositon Staurolite is a metamorphic mineral common in medium grade micaceous schists and gneisses. It has composition Fe2Al9Si4O23(OH). Identification Keys to identification are staurolite's yellow color and pleochrosim, and its occurrence in medium grade pelitic rocks. Important properties  ·Appearance and habit - Staurolite has diagnostic pleochroic yellow color. It often contains many quartz inclusions, sometimes giving a "swiss cheese" appearance.  ·Interference colors - interference colors may range up to 1st order red but are often masked by the strong color of the mineral.  ·Twinning - penetration twins are common but rarely can be seen in thin section Similar minerals:  ·Staurolite is sometimes confused with tourmaline (but tourmaline is uniaxial), and occasionally with epidote (but epidote generally shows higher order interference colors).

Staurolite with Fibrous Sillimanite (Fibrolite) This sample, from near Poughkeepsie, New York, contains a large yellow mass of staurolite on the left hand side (PP). The material to the right of the staurolite is mostly a mix of granular quartz and fine fibrous sillimanite. Some of the sillimanite shows upper second order interference colors but most is so fine grained that interference colors are hard to see. Minor muscovite is also present. The field of view is about 3.5 mm.

Staurolite, Muscovite and Graphite This sample, from western Vermont, contains a large somewhat moth-eaten euhedral yellow staurolite surrounded by a lower-relief mat of clear muscovite and scattered opaque graphite (PP). In PP light, the staurolite has low order interfernce colors (the view is nearly down an optic axis) while the muscovite shows upper order pastels of various hues. The field of view is about 3.5 mm.

Staurolite This sample contains staurolite mounted in epoxy. The largest staurolite (2 mm across) contains many quartz inclusions, showing a classic "Swiss cheese" texture, typical of staurolite.

Staurolite in a Quartzite This view shows a large mass of yellow starurolite surrounded by clear quartz (PP). The staurolite has a radiating habit, not uncommon for this mineral. The minor opaque mineral is magnetite, and hematite stains some of the cracks. This sample comes from Rio Arriba County, Mexico. The field of view is about 2.5 mm across.