Disthene

Disthene, also known as kyanite, was an abundant ornamental stone within the Realms.

Description
The stone could easily be cleaved making it difficult to cut in facets without splitting. Unflawed disthene was difficult to find but came in crystals ranging in color from dark blue to pale green. A typical stone had a base value of 10 gp. Good quality blue facet-grade crystals were the most prized at double the base value for 20 gp.