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.