Helvite group minerals from syenite pegmatites in the Oslo Region, Norway. Contribution to the mineralogy of Norway, No. 68

Most helvite group minerals from the syenite pegmatites in the Oslo Region are manganese rich with
helvite mol% ranging from 65% to 98.5%. From the present investigation on sixteen helvite group
minerals, only two fall in the genthelvite field of the helvite-danalite-genthelvite triangular composition
diagram. Yellow helvite (98-98.5 mol% helvite) from the Saga I quarry at Mørje, Porsgrunn and a very
pale green genthelvite (98 mol% genthelvite) from Bratthagen in Lågendalen are among the purest
helvite group end members hitherto reported. The Saga and Sandøy helvites are the first examples of
ftuorescence among the manganese rich helvites.