[C] Lampblack is an extremely lightweight black powder.
Lampblack in fireworks produces long lasting, very fine dim gold sparks. Primarily in Senko Hanabi sparklers and some long hang time gold streamer and willow stars.
In rockets it's used to opacify rocket fuel grains. The opacifier accelerates the rate of surface burning and prevents infrared energy from penetrating the propellant grain and causing motor pre-ignition.