Coal petrography uses reflected light microscopy and polished sections. Such
sections are made by embedding coal fragments or crushed coal in mounting media.
Samples go through several stages of grinding and polishing to obtain a surface of
adequate quality for microscopic analysis. Above are four photomicrographs (A, B,
C, D) of coals under reflected light in oil immersion: A and B are low rank coals
(lignite and subbituminous rank), showing distinct woody tissue; C is high rank coal
(anthracite), botanical details are no longer visible; D is thermally altered coal close
to a volcanic intrusion.
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