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Anthophyllite thin section

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About Anthophyllite
From Neo-Latin anthophyllum, meaning clove, in allusion to the clove-brown color of the mineral.
Anthophyllite hand-specimen
Formula: ▯Mg2Mg5Si8O22(OH)2
System: Orthorhombic
Color: White, greenish grey, etc.
Lustre: Vitreous, Pearly
Hardness: 5½–6
Density: 2.85–3.57
XPL
XPL
XPL
PPL
PPL
Anthophyllite #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Anthophyllite #2 thin section (hFOV 2mm)
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Anthophyllite PPL properties
Relief: Moderate positive
Habit/Form: Commonly found as euhedral to subhedral columnar, bladed, or acicular crystals, with diamond-shaped cross section typical of amphiboles. Sometimes found as fine to coarse radiating aggregates. There also is an asbestiform variety.
Color: Colorless, clove-brown (Fe), yellowish brown (Fe), grayish brown (Fe), colorless, brown-gray (Fe), brownish (Fe), clove-brown (Fe), dark brown (Fe), grayish-green (Fe)
Pleochroism: None; some of the colored varieties show pleochroism.
Cleavage: Good in two directions {110} – in two directions are at nearly obtuse angles (124° with 56°), and in one direction for longitudinal section. Sections parallel to (100) which display no cleavage since both cleavages are at too acute an angle to the section to be visible. Cross fractures are common.
Anthophyllite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I yellow to order II vivid green
Extinction angle: Parallel / 0° / straight in longitudinal sections, in cross sections symmetrical to outline or cleavage.
Twins: Absent
Uniaxial/Biaxial: Biaxial (+)
Optic axial angle (2V): 2V measured: 57 – 90°, calculated: 82 – 90°
Anthophyllite 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