| General Formula: Al2SiO5 |
Sample: PT-51 | System: Triclinic |
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| TITLE Two kyanite porphyroblasts, within a pelite from the Grenville Province, showing euhedral shapes and the presence of cleavage, evident in the lower grain. Field of View 2.7 mm, plane light |
TITLE The kyanite porphyroblasts have inclusions of quartz and the muscovite fabric is evident between the lower grain and the bottom of the image. Field of View 2.7 mm, crossed polars |
Block diagram showing the relationship between the crystallographic axes and the indicatrix axes. |
Optical Properties
| Colour Pleochroism |
colourless, possibly pale blue non pleochroic |
Form | elongated bladed or columnar crystals |
| Relief RI |
high positive nalpha= 1.710-1.718 nbeta= 1.719-1.725 ngamma= 1.724-1.734 |
Cleavage | one perfect cleavage on {100} and one good cleavage on {010}, a basal parting on {001} may be conspicuous cutting at ~85° |
| Birefringence Interference Colours |
0.012-0.016 first order colours |
Twinning | rare |
| Interference Figure Optic Sign 2V |
biaxial negative 78-84° |
Optic Orientation | inclined extinction with a maximum angle of 30°, length slow |
| Composition | relatively pure Al2SiO5 with minor Fe3+, Ti4+ or Cr3+ | Alteration | may alter to sericite and or chlorite. May be involved in a variety of metamorphic reactions and display reaction textures with andalusite, sillimanite, staurolite, cordierite and garnet. |
| Occurrence | commonn in pelitic schist, gneiss and related metamoprhic rocks. | Distinguishing Features | higher relief, inclined extinction, optical character and elongation |
