guide to thin section microscopy - Mineralogical Society of America
guide to thin section microscopy - Mineralogical Society of America
guide to thin section microscopy - Mineralogical Society of America
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Guide <strong>to</strong> Thin Section Microscopy<br />
Scheme for mineral identification<br />
5. Routine mineral determination<br />
Mineral colour<br />
Observations in plane-polarized light mode<br />
Colour <strong>to</strong>ne and intensity,<br />
Colour distribution<br />
Pleochroism<br />
Ch. 4.2.1<br />
Light refraction<br />
Relief, chagrin,<br />
Becke-Line:<br />
Refractive index n<br />
Ch. 4.2.2<br />
Pleochroism, changing relief/chagrin = anisotropic<br />
non-cubic minerals<br />
Morphological<br />
characteristics<br />
Grain form, twins,<br />
fractures, cleavage,<br />
zoning, inclusions,<br />
decomposition, alteration<br />
Ch. 3.1 – 3.4<br />
Observations in crossed polarizers mode<br />
Mineral <strong>section</strong> remains black during rotation <strong>of</strong> stage<br />
a. isotropic<br />
no optic axis interference figure<br />
Glasses; cubic minerals<br />
b. anisotropic: Section ⊥ optic axis<br />
optic axis interference figure:<br />
uniaxial, biaxial; Ch. 4.2.5<br />
non-cubic minerals<br />
Mineral <strong>section</strong> changes from bright <strong>to</strong> dark during stage rotation = anisotropic<br />
Interference colour<br />
low, high<br />
normal, anomalous<br />
Ch. 4.2.3<br />
Sections <strong>of</strong> maximum<br />
interference colour<br />
Sections with low<br />
interference colour<br />
Morphological features<br />
Twins and intergrowths;<br />
Subgrains, undulose extinction;<br />
Zoning, unmixing;<br />
Brewster crosses in spherulites<br />
Ch. 3.3, 3.4, 4.2.3<br />
Raith, Raase & Reinhardt – February 2012<br />
birefringence<br />
Ch. 4.2.3<br />
orthorhombic<br />
monoclinic<br />
Extinction<br />
straight<br />
symmetrical<br />
inclined<br />
a. optically uniaxial, optic sign<br />
Sections ~ ⊥ opt. axis<br />
b. optically biaxial, optic sign<br />
Sections ~ ⊥ acute bisectrix, or ⊥ optic axis<br />
Ch. 4.2.5<br />
hexagonal<br />
trigonal<br />
tetragonal<br />
triclinic<br />
Sign <strong>of</strong> elongation: l (+), l (-)<br />
Ch. 4.2.4<br />
Extinction angle ε<br />
Ch. 4.2.4<br />
127
Change language