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Bronzite thin section

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About Bronzite
Named in allusion to its bronzelike appearance, especially on cleavage surfaces.
Bronzite hand-specimen
Formula: (Mg, Fe2+)2Si2O6
System: Orthorhombic
Color: White, yellowish green, dark brown to black, greenish white or grey, olive-green
Lustre: Vitreous, Pearly
Hardness: 5–6
Density: 3.2–4.0
XPL
XPL
XPL
PPL
PPL
Bronzite #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Bronzite #2 thin section (hFOV 2mm)
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Bronzite PPL properties
Relief: Moderate positive
Habit/Form: Euhedral crystals are usually stubby prisms. Basal sections are four or eight sided and show the prismatic cleavages intersecting at nearly 90°. Longitudinal sections are usually roughly rectangular and show only one direction of cleavage. Orthopyroxene also forms anhedra, irregular grains occupying the space between other minerals, and pokiloblastic with numerous inclusions of associated minerals. Fibrous orthopyroxene may form reaction rims around other minerals such as olivine or garnet.
Orthopyroxene commonly contains exsolution lamellae of augite. The lamellae may be uniform and tabular, or they may pinch and swell and form rows of blebs. Lamellae of plagioclase in orthopyroxene are sometimes found in anorthositic rocks and apparently formed by exsolution.
Color: Colorless, slight brownish or grayish tinge
Pleochroism: Absent or weak at the Fe-member (from greenish to pale reddish)
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.
Bronzite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I – II
Extinction angle: Parallel / 0° / straight in longitudinal sections and symmetrical in basal sections
Twins: Simple and lamellar twinning on {100} and {001}
Uniaxial/Biaxial: Biaxial (-)
Optic axial angle (2V): 2V measured: 2V 125 – 53 -125°
Bronzite 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