NJG64-3-06
1984
Julgoldite from Tafjord, Sunnmøre. Contribution to the Mineralogy of Norway, No. 67.
64
3
251-255

Julgoldite occurs in open fissures in a Precambrian granitic gneiss situated between Tafjord and Fjøra. Mineral growth in the fissures started under medium or low grade conditions and was completed, after a break, under very low grade conditions. The julgoldite-bearing association consists of calcite + quartz ± chlorite ± laumontite ± babingtonite ± julgoldite ± hematite ± titanite. Julgoldite crystals are very scarce and are found as small inclusions in calcite crystals or in equilibrium with calcite + laumontite ± titanite. The composition of this julgoldite (s.s.) is intermediate, ranging from 62% to 86% of the julgoldite component, and with an average composition corresponding to the form ula (Ca7.88Na0.17) ((Fe2+, Fe3+)3.62Mn0.05Mg0.27) (Fe3+5.75Al2.25) (Si11.76Al0.24O43.21-39.59) (OH)12.8O-36.41· The large cell size of this mineral from Tafjord is indicative of extensive substitution of Fe2+ for Fe3+ and hence a low oxidation state.

0029-196X
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