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| Formula | Ca(Mg,Fe)Si2O6 |
| | Optic class & sign | Biaxial positive |
| | Optical orientation | a near X, b = Y, c at a high angle to Z |
| | Optical plane | (010) |
| | Relief | High |
| | Refractive indices | nx = 1.664 -1.732
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ny = 1.672 -1.739
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nz = 1.694 -1.757
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| n increases with increasing Fe2+ (and Fe3+) |
| | Birefringence (max.) | 0.024 - 0.031 |
| | | Δn decreases with increasing Fe2+; Δn decreases with increasing Al |
| | Optic Angle
| 2Vx
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| | 2Vz
= 49 - 64° |
| | Sign of elongation | Due to large angle between c and Z, not readily applicable |
| | Interference figure | Sections ⊥ c show off-centre figures with few isochromes |
| | Colour / pleochroism | Colourless to pale green; hedenbergite bluish to brownish green
Pleochroism: colour and pleochroism increase with increasing Fe from weak to strong. Chrome diopside is vivid green and distinctly pleochroic.
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| | Zoning | |
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| Form | Habit | Granular, stubby-prismatic, also acicular |
| | | Surface | Anhedral to euhedral |
| | Cleavage | 2 sets {110} distinct, at 93 and 87° (seen in sections ⊥ c); parting on {001} and {100}; parting on (100) may be particularly prominent. In prismatic sections, the traces of the two principal cleavage sets are parallel. |
| | Twinning | Simple or multiple on {100} and {001} |
| | Extinction | Inclined, cɅZ = 38- 48° in (010) sections; c ∥ cleavage traces and prism faces. In the absence of (001) crystal faces, parting on {001} allows to identify the obtuse angle β within which Z is located. Symmetrical extinction to {110} cleavage and {110} faces in sections ⊥ c. |
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| Reaction textures | Late-magmatic hydration to form Ca-amphibole; metamorphic reactions replacing Ca-pyroxenes by Ca-amphiboles |
| | Alteration / decomposition | Secondary amphiboles (tremolite-actinolite), chlorite |
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| Occurence | Ign | Anorthosite, olivine basalt, picrite; ultramafic rocks: chromian diopside in peridotites, pyroxenites, komatiites, kimberlites |
| | | Met | Calcsilicate rocks, skarns, amphibolites, mafic granulites |
| | | Sed | |
| | | Hyd | |
| | | Other | |
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| Distinctive properties | Moderate Δn, large extinction angles in maximum birefringence sections, characteristic pyroxene cleavage observed in sections ⊥ c. Optical properties similar to augite. |
| | Additional comments | Unmixing of orthopyroxene lamellae may be observed in Ca-pyroxene crystallized at high temperatures |
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