The pseudo-biabsorption of trigonal rock-forming carbonates
- Author(s)
- Eugen Libowitzky
- Abstract
The common trigonal carbonate minerals calcite, magnesite, rhodochrosite, siderite, and dolomite-ankerite display a peculiar pseudo-biabsorption effect under the polarising microscope. The effect that is most intense in siderite, has been described as "pseudo-dichroismin the early literature, and is related to the strong birefringence and the high index of refraction (no) of these carbonates. In detail, it is caused (i) by the preparation method, i.e. strong in usual petrographic thin sections with rough (ground but unpolished) surfaces and missing in double-sided polished sections, (ii) by total reflection of light at fissures, cleavage cracks, twin and grain boundaries, and (iii) by high density of microinclusions resulting in different average transmittance of light in the two polarisation directions. In any of the described cases the apparent absorption is stronger if the electric vector of light vibrates parallel to the ordinary ray and thus parallel to the higher index of refraction (no > ne).
- Organisation(s)
- Department of Mineralogy and Crystallography
- Journal
- Neues Jahrbuch für Mineralogie. Monatshefte
- Volume
- 2
- Pages
- 67-79
- No. of pages
- 13
- ISSN
- 0028-3649
- Publication date
- 2001
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1051 Geology, Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/9105f27c-004b-48b4-8056-64bfed305c04