Eudialyte

Eudialyte occurs in nepheline syenites, alkalic granites and their pegmatites. The Kola Peninsula (including the Khibiny massif, Russia) is the main source of material for cabochons and carvings. Small red facetable crystals come from Mont Saint-Hilaire and the Kipawa complex in Quebec, Canada; Greenland (for example Qaqortoq) yields crystals up to about 1 inch. Other sources include Magnet Cove (Arkansas, USA), Sweden, Brazil, Madagascar and Pilansberg (South Africa).

Eudialyte has a relatively low refractive index (1.591–1.633) with low birefringence, a specific gravity of about 2.74–3.00 and weak pleochroism. Massive material typically shows red eudialyte with black aegirine and white feldspar. Calcium-rich members called eucolite may be uniaxial negative with higher RI and SG. There are no known gem treatments, and synthetic eudialyte is made only for research.

With hardness 5–5.5, eudialyte jewelry needs protective settings and occasional wear. It dissolves in acids, so clean it only with a soft brush, mild detergent and warm water. Pieces under 5 ct are considered safe to wear, but because it is mildly radioactive, store it enclosed and apart from other gems.

The name comes from the Greek eu dialytos, "well dissolved" or "easy to dissolve", alluding to the mineral's easy solubility in acids.