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Barite thin section

About Barite
From Greek word meaning heavy, in allusion to its relatively high specific gravity.
Barite hand-specimen
Formula: BaSO4
System: Orthorhombic
Color: Colourless, white, etc.
Lustre: Vitreous, Pearly
Hardness: 3–3½
Density: 4.5
Barite #1 thin section (hFOV 2mm)
Barite #2 thin section (hFOV 2mm)
Barite PPL properties
Relief: Moderate positive
Habit/Form: Crystals are typically tabular or, less commonly, prismatic parallel to the a or b crystal axes. Crystals are often intergrown, forming rosettes or platy aggregates. Barite also forms concretionary masses with fibrous texture, and granular or cleavable masses.
Color: Colorless; can be pale yellow, pale green, pale brown
Pleochroism: None to very weak
Cleavage: In three directions, parallel to {001} and {110} and therefore at angles of 90° and 78°
Barite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order I gray and white to yellow; slightly greater than that of quartz. The maximum interference color is rarely above first-order yellow or orange. The interference colors are frequently mottled.
Extinction angle: Parallel / 0° / straight along {001} cleavage. The extinction in {001} sections is symmetrical.
Twins: Polysynthetic twinning with {110} as the twin-plane is occasionally found.
Uniaxial/Biaxial: Biaxial (+)
Optic axial angle (2V): 2V measured: 36 – 42°, calculated: 36 – 40°
Barite 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