Hydroxycalciopyrochlore from a regionally metamorphic marble at Bližná, Southwestern Czech Republic
Drábek, Milan; Frýda, Jiří; Šarbach, Michal; Skála, Roman
published: Jan 1, 2017
We describe an unusual occurrence of hydroxycalciopyrochlore in marble exposed in the Václav graphite mine at Bližná, southern Czech Republic. Roundish grains attain up to 3 cm, and euhedral crystals are up to 2 mm across. An empirical formula, calculated on the basis two B atoms per formula unit (pfu), is: (Ca0.48 Na0.02 Mg0.06 Mn0.01 Y0.06 ΣREEs0.27 Th0.27 U0.01)Σ1.12 (Nb1.06 Ti0.79Fe0.14 W0.01)Σ2 (O4.96 OH1.04)Σ6 (OH)0.81 · H2O. The associated minerals, in addition to the rock-forming minerals calcite, phlogopite and edenite, include ilmenite, magnetite, euxenite, uranoan thorite, rutile, zircon, molybdenite, chalcopyrite, galena, sphalerite, pyrite, pyrrhotite, barite and apatite. This is the first occurrence of a pyrochlore-group mineral in regionally metamorphosed marble. The assemblage is considered to represent a metamorphosed carbonate-dominated sediment containing evaporitic horizons and vol canic detritus. Now give the reader an explanation, what makes it carbonatite-like?