Dolomite carbonatite
Dolomite carbonatites are igneous rocks that belong to the group of carbonatites . They consist of more than 50 percent by volume dolomite . Dolomite carbonatites can be further subdivided into Beforsite and Rauhaugite .
Definition and initial description
Dolomite carbonatites are defined by the modal dolomite content, which must be more than 50 percent by volume. They were scientifically described for the first time in 1935 by Walter Ehrenreich Tröger .
mineralogy
The main mineral in dolomite carbonatites is by definition dolomite, which is represented with more than 50 percent by volume. The sometimes iron-rich dolomite can also be partially replaced by ankerite or dolomitic ankerite, for example in the dolomitic-anchoritic beforsite in Schelingen in the Kaiserstuhl .
Other carbonates are calcite , magnesite , siderite and magnesium- rich siderite. These are usually joined by apatite , barite , magnetite , orthoclase rich in sodium , titanite , biotite , quartz and sulphide minerals , more rarely also melilite and riebeckite .
Accessories are pyrochlore (also rich in uranium ), columbite , monazite , zirconium , phlogopite , amphibole ( e.g. magnesium-rich arfvedsonite ) and niacolite .
Chlorite acts as an alteration mineral .
Cavities in the rock can be filled with carbon dioxide .
Chemical composition
As an example for the chemical composition of dolomite carbonatites, the Beforsit from Alnön may serve:
| Weight% | Beforsit from the Alnö complex |
|---|---|
| SiO 2 | 6.12 |
| TiO 2 | 0.68 |
| Al 2 O 3 | 1.31 |
| Fe 2 O 3 | 6.94 |
| MnO | 0.75 |
| MgO | 12.75 |
| CaO | 29.03 |
| Na 2 O | 0.14 |
| K 2 O | 0.79 |
| P 2 O 5 | 2.66 |
| CO 2 | 37.03 |
| BaO | 0.11 |
| SrO | 0.0.10 |
Individual evidence
- ^ WE Tröger: Special petrography of igneous rocks . Publishing house of the German Mineralogical Society, Berlin 1935, p. 360 .