|Publication Type:||Journal Article|
|Year of Publication:||2015|
|Authors:||J. Svejkovský, Pauliš, P., Malíková, R.|
|Journal:||Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze|
|Keywords:||Czech Republic, Mokrá near Žlutice, nordstrandite, powder X-ray diffraction data, unit-cell parameters|
The active quarry Mokrá near Žlutice is a very interesting locality, where the first macroscopic samples of Al hydroxides in volcanic rocks in the Czech Republic were found. Besides previously identified böhmite and gibbsite, a macroscopic aggregates of nordstrandite were found. Nordstrandite occurs there in several generations and forms. It mostly creates yellowish to brownish hemispherical aggregates up to 8 mm with surface formed by thin tabular crystals. In smaller cavities, the mineral occurs in the form of groups of small straw-yellow and translucent tabular crystals forming fan- or hedgehog-like irregular aggregates with a size up to 5 mm. A different form of nordstrandite is represented by a light beige to white compact mass with conchoidal fracture and dull lustre similar to opal. The unit-cell parameters of nordstrandite, refined from powder X-ray data, are: a 5.10(2), b 5.07(2), c 5.12(2) Å, α 70.5(3), β 73.8(3), γ 58.2(3)° and V 2061(5) Å3.
Nordstrandit z kamenolomu Mokrá u Žlutic (Česká republika)