Abstract
Orbicular granite near Jelenia Góra in southwestern Poland: the first outcrops?In 1802, Leopold von Buch described some outcrops of orbicular granite in the Karkonosze granite, Lower Silesia, Poland. In that publication, Abraham Gottlieb Werner wrote a foreword dated 1800. The Silesian discovery predates that of the well-known orbicular diorite (Napoleonite) in outcrop on Corsica and, thus, may be the first ever record of this distinctive rock type in its geological context. The characterizing, closely-packed, simple orbs comprise K-feldspar cores surrounded by rims of radiating K-feldspar and quartz. Rapid growth from a hydrous, pegmatitic melt is indicated. The Karkonosze outcrop, in the timing of its discovery, is a unique part of the geological heritage.
Highlights
Among granites, diorites and gabbros, orbicular varieties are some of the most striking
In 1802, Leopold von Buch described some outcrops of orbicular granite in the Karkonosze granite, Lower Silesia, Poland
The second aim is to reintroduce the work of some Polish and some German geologists to the discussion of orbicular granite – work that for reasons of language, place-name evolution and political history, is rarely referenced
Summary
Diorites and gabbros, orbicular varieties are some of the most striking. Orbicular granites and diorites typically occur as minor bodies near to the mixed margins of larger granite and diorite intrusions; many occurrences are known worldwide. In typical examples of the texture, the characterizing orbs comprise a core that is granitic, an enclave, or a single mineral grain surrounded by a rim of radiating feldspar with quartz. This paper concerns an outcrop(s) of orbicular pegmatite in the Karkonosze (Riesengebirge in German) granite intrusion of Carboniferous age in the Polish Sudetes. The second aim is to reintroduce the work of some Polish and some German geologists to the discussion of orbicular granite – work that for reasons of language, place-name evolution and political history, is rarely referenced. The early accounts of Hatch (1888) and Cole (1916) of the orbicular granite at Mullaghderg, Ireland, prompted this examination of the history of the Polish occurrence
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