Black stones of unknown origin have been used in the construction of several structures throughout the known world. Some of it is described as oily or greasy, while others resemble the fused dragonstone of the Valyrian Freehold.
Harrenhal has massive walls of black stone and Stonehelm has watchtowers of black and white stone, but the material of these castles has not been described as unusual by scholars. Additionally, black basalt has been used as another construction material.
Oily black stone
According to the ironborn, the Seastone Chair was found on the shore of Old Wyk and had been carved from a block of oily black stone. Its creators are unknown; Maester Kirth suggests it was left by visitors from across the Sunset Sea. The priests of the Iron Islands claim the ironborn are not descended from the First Men but instead came from the watery halls of the Drowned God beneath the sea. Maesters reject this suggestion that the ironborn are closer to fish or merlings.
Yeen, an ancient ruined city in Sothoryos, is made out of massive blocks of oily black stone. Despite being surrounded by jungle and having been empty for thousands of years, no plant creeps into Yeen.
Isle of Toads
The Isle of Toads, one of the Basilisk Isles, is home to the Toad Stone, a large statue of a toad made of a greasy black stone. It is said the people of the island are reminiscent of fish and have webbed appendages.
Fused black stone
The foundation of the Hightower on Battle Isle at Oldtown is a square, labrynthine fortress of fused black stone. Its appearance is reminiscent of the dragonroads of the Valyrian Freehold and the Black Walls of Volantis, a Valyrian colony, but there is no archaeological evidence of Valyrians at Oldtown, save for the settlers atop Whispering Sound—Valyrians, Ghiscari and Summer Islanders—who set up a place to trade and repair their ships. However, the fortress is plain and unadorned, unlike the fused stone constructions of the Valyrians, who twisted and shaped the fused stone to ornament their buildings.
Archmaester Quillion suggests a connection between the fortress and the mazemakers of Lorath. The legends of Lorath claim the mazemakers were destroyed by something from the sea. Maester Theron, a bastard of ironborn ancestry, suggests in his Strange Stone that there is a connection between the Hightower's base and the Seastone Chair, and that they were created by the Deep Ones, a legendary race created by the breeding of sea creatures with humans and which may have inspired the legends of merlings.
The Five Forts along the northeastern edge of Yi Ti are made of great slabs of single-fused black stone, similar to that of Valyrian construction. Like the Hightower, however, there is no known connection between Valyria and the Five Forts, which are attributed to the legendary Pearl Emperor.
The Bloodstone Emperor rejected the traditional gods of Yi Ti and instead encouraged the worship of a black stone said to have fallen from the sky. This emperor is said to have founded the Church of Starry Wisdom and possibly caused the start of the Long Night.
- The World of Ice & Fire, The Iron Islands.
- The World of Ice & Fire, Beyond the Free Cities: Sothoryos.
- The World of Ice & Fire, Beyond the Free Cities: The Basilisk Isles.
- The World of Ice & Fire, The Bones and Beyond: Asshai-by-the-Shadow.
- A Dance with Dragons, Chapter 5, Tyrion II.
- Fire & Blood, Aegon's Conquest.
- The World of Ice & Fire, The Stormlands: The Men of the Stormlands.
- A Game of Thrones, Chapter 55, Catelyn VIII.
- A Clash of Kings, Chapter 26, Arya VI.
- The World of Ice & Fire, Ancient History: The Dawn Age.
- The World of Ice & Fire, The Reach: Oldtown.
- The World of Ice & Fire, The Free Cities: Lorath.
- The World of Ice & Fire, The Bones and Beyond: Yi Ti.