A Hydrated Barium Silicate in Unmetamorphosed Sedimentary Rocks of Central North Greenland

U. H. Jakobsen
Institute of General Geology, University of Copenhagen, Øster voldgade 10, DK-1350 Copenhagen K. Denmark

Abstract: A new occurrence of barium silicates has been found in unmetamorphosed sedimentary rocks of central North Greenland. Two different barium minerals have been identified, the Ba-feldspar hyalophane, and an unknown and hitherto undescribed hydrated Ba-silicate with an anhydrous chemical composition identical to cymrite but with about 4 moles of water in the mineral structure. Both silicates are found in a black organic-rich chert sequence in close association with baryte. No replacement textures are observed between the three Ba-minerals.

The hydrated Ba-silicate in the unmetamorphosed rock sequence of the Navarana Fjord area is considered to represent a member in a sequence of Ba-silicates from the unknown Ba-silicate with four H2O in the structure (BaAl2Si2O8·4H2O), through cymrite with one H2O (BaAl2Si2O2O8·H2O) to celsian with none (BaAl2Si2O8). This sequence might reflect the continuous release of water during prograde diagenesis and metamorphism. The association between chert and Ba minerals in the sedimentary rocks of the Navarana Fjord area is believed to reflect an addition of silica and barium by hydrothermal solutions.

Keywords: Hydrated Ba-silicate • hyalophane • baryte • unmetamorphosed sedimentary rocks • chert • hydrothermal activity • diagenesis

Mineralogical Magazine; March 1990 v. 54; no. 374; p. 81-89; DOI: 10.1180/minmag.1990.054.374.08
© 1990, The Mineralogical Society
Mineralogical Society (www.minersoc.org)