Kyanite

Kyanite is very rare as a faceted gem, especially if free from inclusions and flaws. The material is extremely difficult to cut because of its perfect cleavage and the extreme variability in hardness in different directions in the same crystal. A few catseye kyanites are known to exist.

Gems have been cut up to about 20 carats: they are seldom completely clean over 5 carats, however Many of these stones are Brazilian; some are African.

Name: From the Greek kyanos, meaning blue.

Read more about Kyanite:

https://www.gemsociety.org/article/kyanite-jewelry-and-gemstone-information/