A magical explosive of powerful magnitude. First seen as a blue bottled potion gifted by Tarik Nowlin.

“We’ll need this at the gate.” - Tarik Nowlin, Battle at Blacklake (RPA-ADV1) 

Tarik gives you a bottle of Bluestone Fireball to destroy the gate to the Dragul outpost outside Blacklake.

If attempted to open the bottle at Tarik's campsite, he is quick to intervene, explaining its combustible nature;

“Any exposure to air and the fireball will explode, which would be very loud and could easily kill us. Let’s try to stay quiet and alive. Save the fireball for the gate.” - Tarik Nowlin, Battle at Blacklake (RPA-ADV1)

Rose of the Starlit Door used the same material in a powder form to blast a hole in Taron's Arena;

You question the merchant further and learn that a Halfling woman with a strange ring planted a satchel near the wall and then ran off before anyone was the wiser.

You notice traces of explosive bluestone powder on her shoes, and you see the Starlit Door insignia on her ring. It seems Rose had a role to play in the cult’s plot against Sabek. - Eye of Ulos (RPA-ADV4)

Some investigative work uncovers a different composition from the potion Tarik gave you at Blacklake;

It’s likely a mixture of trungle grit and bluestone that someone used to assemble an explosive device. - Eye of Ulos (RPA-ADV4)