is a Sodium Aluminum Fluoride with formula Na3AlF6 and hardness of 2.5.
Essentialy has ben used in the past as fsolvent for aluminum rich ore and it was an excellent flux,but now became very rare and too expensive for this purpose. It’s low refractive Index make it disapper when immersed in water,even when is not completely transparent,it really looks like a piece of ice. Unusual facet stones for collector.
Size: 9x11x6.6 mm.
Weight: 4.03 ct.