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Enstatite-Ferrosilite thin section

About Enstatite-Ferrosilite
Enstatite – from Greek for opponent, because of its refractory nature before the blowpipe. Ferrosilite – from composition, iron (ferrous) and silicate.
Enstatite-Ferrosilite hand-specimen
Formula: Mg2Si2O6 – Fe2Si2O6
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
Enstatite-Ferrosilite #1 thin section (hFOV 2mm)
Enstatite-Ferrosilite #2 thin section (hFOV 2mm)
Enstatite-Ferrosilite #3 thin section (hFOV 2mm)
Enstatite-Ferrosilite 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 anhedral, irregular grains occupying the space between other minerals, and poikiloblastic 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 greenish or grayish tinge. Color increase with Fe.
Pleochroism: Absent or weak at the Fe-member (see Bronzite)
Cleavage: Good in two directions {110} (at right angles to the c-axis – on (001)) – the cleavage 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.
Enstatite-Ferrosilite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I gray or white to high order I; the maximum interference color is pale yellow of the first order.
Extinction angle: Parallel / 0° / straight in longitudinal sections and symmetrical in basal/cross sections.
Twins: Simple and lamellar twinning on {100} and {001}
Uniaxial/Biaxial: Biaxial (+/-)
Optic axial angle (2V): 2V measured: 54 – 90°, calculated: 58 – 86°
Enstatite-Ferrosilite 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