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Tremolite thin section

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About Tremolite
Locality in Tremola Valley, near St. Gotthard, Switzerland.
Tremolite hand-specimen
Formula: ▯Ca2Mg5 Si8O22(OH)2
System: Monoclinic
Color: White, brown, colourless, grey, light green, green, light yellow, pink-violet
Lustre: Vitreous, Silky
Hardness: 5–6
Density: 2.99–3.03
XPL
XPL
XPL
PPL
PPL
Tremolite #1 thin section (hFOV 2mm)
XPL
XPL
XPL
PPL
PPL
Tremolite #1 thin section (hFOV 2mm)
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Tremolite PPL properties
Relief: Moderate positive
Habit/Form: Commonly as columnar, bladed, or acicular crystals elongate parallel to the c axis. Sometimes fibrous or asbestiform. Basal sections are diamond shaped and show the typical amphibole cleavage. Longitudinal sections (parallel to the c axis) are roughly rectangular and show only one cleavage trace.
Color: Colorless
Pleochroism: Absent or very weak
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.
Tremolite XPL properties
Isotropy/Anisotropy: Anisotropic
Interference color: Order II green
Extinction angle: Basal sections show symmetrical extinction. The extinction angle of 17 to 21° is seen in sections parallel to (010). Sections parallel to (100) show parallel extinction. Extinction angles show a general decrease with increasing iron content (from tremolite to actinolite and finally to ferro-actinolite).
Twins: Simple and lamellar twins on {100}
Uniaxial/Biaxial: Biaxial (-)
Optic axial angle (2V): 2V measured: 88 – 80°, calculated: 82 – 84°
Tremolite 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