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Photomicrograph of a mostly omphacite in plane polarized light. Click on the thumbnail to see a larger ppl/xpl rollover image. |
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| Formula | (Ca,Na)(Mg,Fe2+,Fe3+,Al)Si2O6 |
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| Crystal System | monoclinic | 2/m |
| Crystal Habit | stubby crystals, most common as anhedral grains | |
| Cleavage | good cleavage on {110}, intersect at 87 and 93° (similar to other pyroxenes), parting on {100} | uneven to conchoidal fracture, brittle |
| Color/Pleochroism | Color in Hand Sample: green to dark green Color in PPL: colorless to pale green Pleochroism: weakly pleochroic, Z=very pale green to blue green |
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| Optic Sign | Biaxial (+) | |
| 2V | 56-84° | normal range for 2V= 60-75° |
| Refractive Index
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alpha=1.662-1.701 |
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| Distinguishing Features | High relief in thin section. Characteristic pyroxene cleavage. Gray streak. Hardness = 5-6. |
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| Occurrence | Commonly found in rocks that formed in high-pressure conditions, such as eclogite, a high-pressure metamorphic/igneous rock. It is less commonly found in alpine metamorphic belts in blue schist, metagraywacke, and can also be found in granulites. |
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| Editors | Anna Lavarreda ('08j) | |
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Photomicrograph of a mostly omphacite in plane polarized light. Click on the thumbnail to see a larger ppl/xpl rollover image. |