Is a Magnesium Fluoride with formula MgF2 and hardness of 5-6.
It's crystals are generally very small and brittle, is rare to find a clean stone over 1 ct.
The best gem material comes from Brazil, and is quite expensive; this gem here instead comes from Grube Clara,Oberwolfach,Black Forest, Baden-Wurttenberg,Germany and is an aggregate of tiny acicular crystals.
Size: 9x7x3.8 mm.
Weight: 1.03 ct.