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Diopside thin section

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About Diopside
From Greek for two and view, since the vertical prism zone apparently can be oriented in two ways.
Diopside hand-specimen
Formula: CaMgSi2O6
System: Monoclinic
Color: Light to dark green, blue, brown, colourless, snow white, grey
Lustre: Vitreous, Dull
Hardness: 5½–6½
Density: 3.22–3.38
XPL
XPL
XPL
PPL
PPL
Diopside #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Diopside #2 thin section (hFOV 2mm)
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Diopside PPL properties
Relief: High positive
Habit/Form: Crystals are usually stubby prisms elongate along the c axis. Basal cross sections are four or eight sided and show the two cleavages at ~87°. Longitudinal sections are roughly rectangular and show only one cleavage direction. Augite also forms anhedral grains, or irregular masses that may enclose associated minerals. Overgrowths of hornblende are relatively common. Lamellae of exsolved orthopyroxene are commonly found parallel to {100} , whereas pigeonite lamellae are inclined somewhat to either P100} or {001}. The lamellae may be inclined up to 22 and 17° from (100) and (001) respectively for Mg-rich augite. Smaller inclinations are found in Fe-rich augite.
Color: Diopside (Mg-member) is colorless; Hedenbergite (Fe-member) is pale green to bright-green/yellow-green
Pleochroism: For Diopside is absent; with increasing Fe2+, pleochroism also appears.
Cleavage: Good in two directions {110} (at right angles to the c-axis – on (001)) – the clivage angle in two directions are at nearly right angles 87° and 93°.
Prismatic sections parallel to (100) or (010) to which both cleavages are at too acute an angle to be always visible, especially in slightly thick sections.
Diopside XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I-II; bright
Extinction angle: The maximum extinction angle in sections cut parallel to the c axis varies from 38° to 45°. In cross sections the extinction is symmetrical to the cleavage traces. In {100} sections the extinction is parallel.
Twins: Simple or polysynthetic twinning is relatively common on {100} or {001}.
Uniaxial/Biaxial: Biaxial (+)
Optic axial angle (2V): 2V measured: 58 – 63°, calculated: 56 – 64°
Diopside distinguishing features under the microscope
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References
  • Deer, W. A., Howie, R. A., & Zussman, J. (2013). An introduction to the rock-forming minerals (pp. 498). Mineralogical Society of Great Britain and Ireland, London.
  • mindat.org – The Mineral Database