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Wollastonite thin section

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About Wollastonite
Wollastonite is one of the most important minerals within the pyroxenoid group, among rhodonite and pectolite. Like the pyroxenes, the pyroxenoid frame is a single chain, but the individual tetrahedra are twisted relative to those in the pyroxene chain. Wollastonite is named in 1818 by J. Léman in honor of William Hyde Wollaston (1766-1828), an English mineralogist and chemist.
Wollastonite hand-specimen
Formula: CaSiO3
System: Triclinic
Color: White, gray-white, light, etc.
Lustre: Vitreous, Pearly
Hardness: 4½–5
Density: 2.86–3.09
XPL
XPL
XPL
PPL
PPL
Wollastonite #1 thin section (hFOV 2mm)
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XPL
XPL
PPL
PPL
Wollastonite #2 thin section (hFOV 2mm)
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XPL
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PPL
PPL
Wollastonite #3 thin section (hFOV 2mm)
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Wollastonite PPL properties
Relief: Moderate positive
Habit/Form: Usually bladed, columnar, or fibrous; elongate parallel to the b axis, and flattened parallel to {100} or {001}
Color: Colorless or turbid owing to many small inclusions (gas?). Coarse pieces are colorless, gray, or pale yellow
Pleochroism:
Cleavage: Perfect on {100}, good on {001} and {-102}
Wollastonite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I red; the maximum interference color is about orange of the first order. Longitudinal sections show gray or white interference colors
Extinction angle: Almost parallel / 0° / straight in longitudinal sections (3-5°), oblique in cross sections (30-44°)
Twins: Twins with {100} as twin-plane are known
Uniaxial/Biaxial: Biaxial (-)
Optic axial angle (2V): 2V measured: 36 – 60°
Wollastonite 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