Wildfire

Clash of Kings
Tyrion V

but they could make wildfire. "Water will not quench it, I am told."
"That is so. Once it takes fire, the substance will burn fiercely until it is no more. More, it will seep into cloth, wood, leather, even steel, so they take fire as well."

Davos III
He grimaced. Burning pitch was one thing, wildfire quite another. Evil stuff, and well-nigh unquenchable. Smother it under a cloak and the cloak took fire; slap at a fleck of it with your palm and your hand was aflame. "Piss on wildfire and your cock burns off," old seamen liked to say.

Tyrion XIII
Motionless as a gargoyle, Tyrion Lannister hunched on one knee atop a merlon. Beyond the Mud Gate and the desolation that had once been the fishmarket and wharves, the river itself seemed to have taken fire. Half of Stannis's fleet was ablaze, along with most of Joffrey's. The kiss of wildfire turned proud ships into funeral pyres and men into living torches. The air was full of smoke and arrows and screams.

Tyrion XIII
A dozen great fires raged under the city walls, where casks of burning pitch had exploded, but the wildfire reduced them to no more than candles in a burning house, their orange and scarlet pennons fluttering insignificantly against the jade holocaust. The low clouds caught the color of the burning river and roofed the sky in shades of shifting green, eerily beautiful. A terrible beauty. Like dragonfire. Tyrion wondered if Aegon the Conqueror had felt like this as he flew above his Field of Fire.

A Storm of Swords

Davos I
He needed air by then, but he was afraid. Was he past the chain yet, was he out in the bay? If he came up under a ship he would drown, and if he surfaced amidst the floating patches of wildfire his first breath would sear his lungs to ash. He twisted in the water to look up, but there was nothing to see but green darkness and then he spun too far and suddenly he could no longer tell up from down

A Feast For Crows
Cersei III

The tower went up with a whoosh. In half a heartbeat its interior was alive with light, red, yellow, orange . . . and green, an ominous dark green, the color of bile and jade and pyromancer's piss. "The substance," the alchemists named it, but common folk called it wildfire. Fifty pots had been placed inside the Tower of the Hand, along with logs and casks of pitch and the greater part of the worldly possessions of a dwarf named Tyrion Lannister.
The queen could feel the heat of those green flames. The pyromancers said that only three things burned hotter than their substance: dragonflame, the fires beneath the earth, and the summer sun.