Hambergite was originally discovered in southern Norway but that material was not clean enough to be considered gem material. The most important current source is probably in Anjanabanoana, Madagascar. Recently, some nice material has also been unearthed in Molo, Myanmar, but most of the crystals are small.
Hambergite has the lowest known density of any gem with such a high birefringence (.072). These unique properties make it easy to identify. Stones have little fire any may resemble quartz but with the high birefringence, hambergite is nearly impossible to misidentify.
R. Webster, 1994, Fifth edition, Gems Their Sources, Descriptions And Identification, Reed Educational and Professional Publishing Ltd.