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Spodumene thin section

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About Spodumene
From Greek for reduced to ashes, either in allusion to its ash-gray color, or the ash-colored mass formed when heated before the blowpipe.
Spodumene hand-specimen
Formula: LiAlSi2O6
System: Monoclinic
Color: Colourless, yellow, etc.
Lustre: Vitreous, Dull
Hardness: 6½–7
Density: 3.1–3.2
XPL
XPL
XPL
PPL
PPL
Spodumene #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Spodumene #2 thin section (hFOV 2mm)
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Spodumene PPL properties
Relief: Moderate-High positive
Habit/Form: Crystals are prismatic with roughly octagonal cross sections that show both cleavages intersecting at about 87°. Also as lathlike acicular crystals and cleavable masses. Because spodumene is usually found in pegmatites, its crystals may be far larger than normal in thin sections.
Color: Colorless; rare pale green. Pale pink (kunzite) and pale green (hiddenite) varieties are rare.
Pleochroism: None to weak (green or lilac)
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.
Spodumene XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I red
Extinction angle: The maximum extinction angle in longitudinal sections varies from 20° to 27°. In cross sections the extinction is parallel or symmetrical. Oriented sections cut parallel to the (100) parting have parallel extinction.
Twins: Twins with {100} as twin-plane are known.
Uniaxial/Biaxial: Biaxial (+)
Optic axial angle (2V): 2V measured: 54 – 69°, calculated: 88°
Spodumene 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