Textural relations and chemical composition of minerals from a pollucite + harmotome + chabazite nodule in the Věžná I pegmatite, Czech republic
| Authors | |
|---|---|
| Year of publication | 2018 |
| Type | Article in Periodical |
| Magazine / Source | Canadian Mineralogist |
| MU Faculty or unit | |
| Citation | |
| Web | http://dx.doi.org/10.3749/canmin.1800014 |
| Doi | http://dx.doi.org/10.3749/canmin.1800014 |
| Keywords | zeolites; pollucite; analcime; harmotome; chabazite; textural relations; replacement; chemical; compositions; pegmatite |
| Description | Minerals and their textural relations from a pollucite + harmotome + chabazite nodule (PHC) enclosed in a volumetrically negligible albite-pollucite unit (1-2 dm(3)) in the Veznz I beryl-columbite pegmatite were examined by EMP and XRD. The albite-pollucite unit consists of a dominant albite-lepidolite-topaz subunit (Ab + Qz + Kf + Ms + Lpd + Tpz) as a matrix surrounding minor nodular subunits: the examined PHC and triplite-apatite nodules. Small vugs with crystals of harmotome and chabazite growing from the PHC nodule and polylithionite with sokolovaite rims, albite, fluor-elbaite, and K-feldspar extending from the host albite-lepidolite-topaz subunit are locally developed at the margin. Several textural/paragenetic types of the individual minerals in the PHC were distinguished from center to margin of the nodule and vugs. The minerals exhibit very complicated textural relations varying from evident replacement of early pollucite by analcime to evident replacement of pollucite-analcime by late zeolites (hannotome + chabazite). Ilowever, the pollucite types have almost identical compositions and underwent strong analcimization along the contact with the albite-lepidolite-topaz subunit. Harmotome evolves from K-rich harmotome I (harmotome > phillipsite-K) via Ca,K-moderate harmotome II to Ca,K-poor and Ba-rich harmotome III and chabazite evolves from Ca-rich chabazite I via slightly K-enriched chabazite Il to moderately K-enriched chabazite III (chabazite-Ca > chabazite-K) from center to margin and vugs, respectively. Pollucite was replaced by the assemblage harmotome + chabazite according to the simplified equation pollucite + Ba + 2Ca + 25 H2O = harmotome + chabazite. The temperatures of the processes leading to the assemblage pollucite + analcime + harmotome + chabazite in the PHC were inferred from the experimental and empirical P-T stabilities of the minerals: primary pollucite T > similar to 350 degrees C, analcimization T < similar to 150 degrees C, harmotome + chabazite T < similar to 100-150 degrees C. |
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