An hydrated Potassium,Calcium sulfate with formula K2Ca(SO4)2-(H2O) and hardness 2.5. Typical evaporite saline mineral or volcanic sublimate; soluble in water. Rarely transparent, often included with lots of impurity. This gem here comes from Kalush ( also called Kalushite) deposit,Ucraina. This gem here is the best we can get. Size:11.2x8.1x4 mm. Weight:2.16 ct. CODE#2827