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Titanite (Sphene) thin section

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About Titanite (Sphene)
Titanite – from composition, contains titanium. Sphene – from Greek for wedge, in allusion to the characteristic habit of the crystals.
Titanite (Sphene) hand-specimen
Formula: CaTiSiO5
System: Monoclinic
Color: Colourless, brown
Lustre: Adamantine, Resinous
Hardness: 5–5½
Density: 3.48–3.6
XPL
XPL
XPL
PPL
PPL
Titanite #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Titanite #2 thin section (hFOV 2mm)
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Titanite (Sphene) PPL properties
Relief: Very High positive
Habit/Form: Euhedral to subhedral grains with a wedge- or diamond-shaped cross section are common, as are rounded or irregular anhedral grains. Radioactive varieties may form pleochroic halos in enclosing biotite, chlorite, or hornblende.
Color: Almost colorless to neutral; tan-brown color or yellow-brown
Pleochroism: Absent to weak
Cleavage: Sphene often has prominent parting (parallel to 221). These parting directions are not parallel to the crystal outlines.
Titanite (Sphene) XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: High-order cream, pearl-gray; or anomalous blue/brown
Extinction angle: Rhombic/diamond sections have symmetrical extinction. Maximum extinction to cleavage traces is 36° to 45°.
Twins: Simple twinning on {100} is common, dividing diamond sections near the long diagonal. Multiple twinning is rare on {221}.
Uniaxial/Biaxial: Biaxial (+)
Optic axial angle (2V): 2V measured: 17 – 40°, calculated: 68 – 82°
Titanite (Sphene) 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