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Formula | Mg2SiO4 | Mg endmember of olivine (Mg,Fe)2SiO4. |
Crystal System | orthorhombic | 2/m2/m2/m |
Crystal Habit | granular masses or rounded, embedded grains | |
Cleavage | Cleavage: indistinct on {010},{100} | conchoidal fracture, brittle |
Color/Pleochroism | Pale, yellow-green to olive-green. Colorless to pale green in thin section. Weak, pale green pleochroism in thin section. | Darker with increasing Fe, moving away from pure forsterite. |
Optic Sign | Biaxial (+) | |
2V | 82-90 | Varies depending on composition. |
Optic Orientation | X=b
Y=c Z=a O.A.P. = (010) |
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Refractive Indices
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1.62-1.64 |
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Extinction | parallel | Elongate crystals display parallel extinction. |
Distinguishing Features | Colorless to olive green in thin section. Second-order interference colors. High relief. Lack of cleavage. H= 6.5-7. G = 3.2. Streak is colorless or white. May be confused with epidote, which has cleavage and a is pistachio-green in hand sample. | |
Occurrence | Occurs in a wide variety of volcanic rocks, both as phenocrysts and as groundmass. Occasionally found in metamorphosed carbonate-bearing rocks (crystalline dolomitic limestones) associated with calcite, dolomite, diopsite, epidote-group minerals, grossular garnet, tremolite, and related Ca-Mg-bearing minerals. | |
Editors | Micehelle Arsenault (01), Jamie Mitchell (03), Angelie Peterson (02), Cheryl Mawaka (04), Stephanie Moore (07), Eli Molitors Bergman (17) |