The pseudo-biabsorption of trigonal rock-forming carbonates

Autor(en)

Eugen Libowitzky

Abstrakt

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(en)

Institut für Mineralogie und Kristallographie

Journal

Neues Jahrbuch für Mineralogie. Monatshefte

Band

2

Seiten

67-79

Anzahl der Seiten

13

ISSN

0028-3649

Publikationsdatum

2001

Peer-reviewed

Ja

ÖFOS 2012

1051 Geologie, Mineralogie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/9105f27c-004b-48b4-8056-64bfed305c04