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Zoisite thin section

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About Zoisite
For Siegmund Zois, Baron von Edelstein (1747-1819), Austrian scholar and writer who was interested in minerals and who financed mineral-collecting expeditions.
Zoisite hand-specimen
Formula: Ca2Al3O(SiO4)(Si2O7)(OH)
System: Orthorhombic
Color: Colourless, purple, greyish-white, grey, yellowish-brown, yellow, pink, green
Lustre: Vitreous
Hardness: 6–7
Density: 3.15–3.36
XPL
XPL
XPL
PPL
PPL
Zoisite #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Zoisite #2 thin section (hFOV 2mm)
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Zoisite PPL properties
Relief: High positive
Habit/Form: Often found as anhedral grains or granular aggregates. Crystals are columnar, prismatic, bladed, or acicular with the long dimension parallel to the b axis. Zoisite may form oriented intergrowths with epidote.
Color: Colorless; but can be pale pink, pale red-violet (V), pink, deep blue (V), pale yellow, yellow-green
Pleochroism:
Cleavage: Perfect in one direction {010}
Zoisite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I gray and white; often anomalous blue interference colors (‘berlin blue’).
Extinction angle: Parallel / 0° / straight in most sections.
Twins: Polysynthetic twinning may be present.
Uniaxial/Biaxial: Biaxial (+)
Optic axial angle (2V): 2V 0 – 69°
Zoisite 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