Beryllium phosphates from the Proterozoic granitic pegmatite at Norro, southern Stockholm archipelago, Sweden
Title:
Beryllium phosphates from the Proterozoic granitic pegmatite at Norro, southern Stockholm archipelago, Sweden
Author:
Nysten, Per Gustafsson, Lars
Appeared in:
GFF
Paging:
Volume 115 (1993) nr. 2 pages 159-164
Year:
1993
Contents:
The early Proterozoic Svecofennian granitic pegmatites at Norro, and Råno, situated 40 km south of Stockholm, carry primary FeMn-phosphates (e.g. triphylite, triplite, wolfeite, sarcopside, graftonite) which have been partly altered to secondary phosphates of the Hagendorf type. The dykes, which both are emplaced in garnet-cordierite bearing veined gneisses, are moderately fractionated as shown by the presence of beryl, columbite, and ruby mica. Beryl from Norro shows progressive alteration into mixtures of hurlbutite/hydroxyl-herderite and hydroxyl-herderite/vayrynenite. Beryllonite was observed in one sample only, intergrown with hurlbutite. Hydroxyl-herderite/hurlbutite occurs partly rimming beryl at Råno. Microprobe analysis shows that beryllonite, hydroxyl-herderite and hurlbutite are close to stoichiometric and vayrynenite from Norro gave: (Mn0.80Fe0.16Mg0.04)0.96Be0.97(PO4)(OH)0.97. Cell dimensions of vayrynenite obtained from Si calibrated XRD are: a = 5. 410(1) Å, b = 14.528(3) Å, c = 4. 714(2) Å, ss = 102.82 (3)° and for hurlbutite from Norro: a = 8. 313(1) Å, b = 8.796(2) Å, c = 7. 809(1) Å, ss = 90.508(9)°. The Be-phosphates may have formed by acid phosphorous fluids, liberated by the breakdown of triphylite, attacking beryl crystals at a late stage of pegmatite formation.
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