Occurrence and Compositon
Kyanite is a metamorphic mineral found in medium or high pressure mica schists and gneisses. Its formula is Al2SiO5.

Keys to identification are high relief, bladed habit, good cleavage and first order interference colors.

Important properties
 ·Relief and habit - Kyanite often appears as high-relief blades with one good cleavage parallel to the long dimension.
 ·Color - Typically colorless but sometimes has a pale blue color. May be slightly pleochroic.
 ·Interference colors - Rarely higher than upper first order.
 ·Extinction angle - extinction may be up to 30o from the cleavage direction, depending on grain orientation.
 ·Interference figure - biaxial (-) with very high 2V.

Similar minerals
 ·Similar to its polymorphs andalusite and sillimanite but has a larger extinction angle than either of them.
 ·Orthopyroxene has a smaller 2V.
 ·Clinozoisite typically has lower birefringence and often shows anomalous interference colors. It also does not develop blades with parallel cleavage and smaller 2V.

Kyanite in Schist from Near Flin Flon, Manitoba

This view has one large blade of kyanite at the center. It is surrounded mostly by (twinned) plagioclase, minor quartz, and flakes of pleochroic brown biotite. A single large garnet (isotropic) is on the right hand edge of the view, just below center. The plagioclase and quartz are difficult to tell appart in at this magnification.

The field of view is about 2.5 mm across.

Kyanite and Quartz, with Minor Muscovite

This veiw includes two kyanite grains/aggregates, one a large blade showing cleavage and the other a patchy mass showing no cleavage. The kyanite is surrounded by quartz. The quartz is clear with low relief and low order interference colors, while the clear kyanite has high relief and interference colors range up to first order yellow. (In some thin sections, kyanite's interference color may be first order reds.) Note the undulatory extinction displayed by quartz. Several flakes of muscovite (clear with low relief and uper second order interference colors) can be seen just to the right of the kyanite.

This view is about 1 mm across.

Kyanite with Minor Quartz and Rutile

This veiw includes mostly kyanite (high relief, cracked/cleaved/fractured). The kyanite shows good cleavage, and some grains are twinned. Its interference colors range up to second order yellow. Minor quartz is present, most notably in the lower right corner of the view. The dark mineral, not quite istropic in these views, is rutile. This view is about 1 mm across.