Kyanite thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope.

At higher temperatures kyanite inverts to sillimianite, over a wide range of pressures and high temperatures. Andalusite, kyanite, and sillimanite are an example of polymorphism because the conditions under which they were formed give rise to their structures.

Photomicrograph of kyanite next to a garnet crystal and surrounded by muscovite in plane polarized light. Kyanite typically displays pale green pleochroism and no distinct cleavage. Click on the image to see a larger image with xpl rollover.

Kyanite in PPL, 5x magnification, 360 degree rotation. Elongated kyanite crystal displaying one cleavage plane and high relief. Surrounded by biotite (red-brown pleochroism), plagioclase (colourless) and quartz (colourless).

microscopic intergrowths of kyanite and staurolite (yellow), PPL and XPL image, 10x (Field of view = 2mm). Panoramic view of staurolite schif from Sardinia, Italy. Image by Andy Tindle ( Virtual Microscope ).

The four kyanite crystals are colorless, have high relief, and two have a strong cleavage parallel to their length. Relief is much higher than muscovite, which surrounds the kyanite. The kyanite crystals have interference colors up to upper 1 st order, much lower than muscovite.

Rotation 1 - Nice kyanite with both cleavage traces sharp. Kyanite has straight extinction to the elongation. Rotation 2 - Strain shadowing and twinning in kyanite.

Kyanite in migmatite from Kaňk near Kutná Hora, the Czech Republic; PPL (left) and XPL (right). Width of fields of view is ca. 0.7 mm. Photo: JiZi.

Kinking is common in minerals with strongly anisotropic crystal structures and consequently only one slip plane, such as biotite, kyanite and enstatite, but also occurs in minerals with several slip systems, such as quartz and olivine.

Optical Properties: Transparent to translucent. Color: Blue, white, rarely green, gray, yellow, pink, black, can be zoned; colorless to pale blue in thin section. Luster: Vitreous to pearly. Optical Class: Biaxial ({). Pleochroism: Weak; in thick sections, X …