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Photomicrograph of a mostly clinozoisite in plane polarized light . Click on the thumbnail to see a larger PPL/XPL rollover image. Under XPL it is the light-bluish gray mineral. |
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| Formula | Ca2Al3O(SiO4)(Si2O7)(OH) |
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| Crystal System | monoclinic; 2/m | |
| Crystal Habit | rounded grains, massive granular (coarse or fine) | |
| Cleavage | {001} perfect and {100} fair to poor. | {001} tends to control fragment orientation |
| Color/Pleochroism | pale green to gray in color, transparent to translucent; not pleochroic. |
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| Optic Sign | Biaxial (+) | |
| Birefringence | 0.004-0.0012 | |
| 2V | 14° - 90° | |
Refractive Index |
alpha = 1.670 - 1.715 beta = 1.674 - 1.725 gamma = 1.690 - 1.734 |
Refractive indices and birefringence increase with iron content. |
| Extinction | Extinction angle to trace of cleavage usually between 0° & 25°. | Sometimes the extinction angle can be as large as 60°. |
| Distinguishing Features | Distinguishable from epidote by optic sign, birefringence, and color. In thin section it has high positive relief. Crystals can be columnar or bladed, and sometimes fibrous and elongate paralles to the b axis. |
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| Occurrence | Favored in more aluminous rocks, and is a common accessory mineral in regional and contact metamorphic rocks. It can be present in quartzite, slate, chlorite schist, mica schist, gneiss, amphibole, marble, skarn deposits, hornfels, phyllite, and calc-silicate. |
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| Editors | Abby D'Ambrosia ('07) | |
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Photomicrograph of a mostly clinozoisite in plane polarized light . Click on the thumbnail to see a larger PPL/XPL rollover image. Under XPL it is the light-bluish gray mineral. |