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Leucite thin section

About Leucite
From Greek for white, in reference to its color.
Leucite hand-specimen
Formula: KAl(Si2O6)
System: Tetragonal
Color: White, grey
Lustre: Vitreous
Hardness: 5½–6
Density: 2.45–2.5
Leucite #1 thin section (hFOV 2mm)
Leucite PPL properties
Relief: Low negative
Habit/Form: Leucite commonly occurs as equant trapezohedral crystals that show eight-sided to nearly round cross sections. It also occurs as small microlites, and skeletal or anhedral grains in the groundmass of volcanic rocks. Inclusions of glass, olivine, magnetite, pyroxene, and other minerals may be present.
Color: Colorless
Cleavage: {110} poor
Leucite XPL properties
Isotropy/Anisotropy: Small crystals may appear isotropic, but large crystals nearly always display a very weak birefringence and complex twin patterns.
Interference color: Order I dark-gray
Extinction angle: isotropic, is often wavy.
Twins: Complicated polysynthetic twinning in several directions (a bit like microcline); often forming concentrically or at 60°
Uniaxial/Biaxial: Uniaxial (+) (anomalous Biaxial)
Optic axial angle (2V):
Leucite distinguishing features under the microscope
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  • 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