Question: what are blue semi precious stones?
Answer: Sapphire. By far the most popular blue gem for faceting, a blue sapphire can have very high saturation. ... 
Tourmaline (Indicolite and Paraíba) ... 
Aquamarine. ... 
Spinel. ... 
Turquoise. ... 
Chalcedony. ... 
Jeremejevite. ... 
Dumortierite.